8 ms·

Testing Phone-Sized Faraday Bags

368 points by jor-el 5y ago

Tronno 5y ago
What's the use case for these products? Even if the radio is blocked, how does that stop a device from collecting data anyway, and exfiltrating it the moment it finds a network? Won't it look for a network the moment you take it out of the bag? And don't you have to remove it from the bag to use it practically? Ultimately, if your device is compromised or untrustworthy to the extent that it has to be policed this way, is it not safer to just... get rid of it?
- sanirank 5y ago
  I still wonder why phone cases with physical blockers for camera and mic aren’t in high demand, and why there aren’t hundreds of pirated copies on the market for the ones that have been developed.
ziggus 5y ago
Solution: Wrap device in aluminum foil, place in Mylar bag, place bag in cookie tin.
docflabby 5y ago
Tinfoil hat on - has anyone considered how suspicious that only the commercial products worked, maybe the post is just a very clever shill for those products?
- tablespoon 5y ago
  > Tinfoil hat on - has anyone considered how suspicious that only the commercial products worked, maybe the post is just a very clever shill for those products? Not really, tinfoil actually worked, but it was apparently too difficult to get right: > In my experiments, I found I could sometimes achieve approximately 90 dB attenuation by carefully wrapping the generator in foil and double folding the seams on all sides, which is quite good (comparable to commercial pouches). This actually matches my experience with a GPS logger. It only had an on/off switch and I wanted to download the track from my trip without getting points from the download location at the end. IIRC, it was still able to get fixes even wrapped in tin foil.
aaroninsf 5y ago
I am happy to see EDEC performed well. Idle comment: we use their smaller keychain bags for car fobs, after hearing with dismay first- and second- hand accounts of relay attacks being used to steal or ransack cars in our neighborhood (94110). We now keep our fobs in them except in use.
Wistar 5y ago
Matt Blaze is a treasure.
wolverine876 5y ago
What is the use case for disabling wireless communication for your phone? How will you use it? How will anyone call you? If you don't want to use wireless functions, buy a tablet that lacks all the radio hardware.
- jagged-chisel 5y ago
  Bad Guys can't follow you using the signal. That's about it. Sure, they can tail you, but that's Work. And they'll know where you are the moment you take it out, but hopefully they're too far away to act on it. All in all, if you NEED something like this, your opec had better include more than this.
  - wolverine876 5y ago
    > Bad Guys can't follow you using the signal. That's about it. Sure, they can tail you, but that's Work. And they'll know where you are the moment you take it out, but hopefully they're too far away to act on it. Why have the phone if it's not connected to the network? It's a communication device. Just leave the phone home.
_0w8t 5y ago
I visited at the end of eighties a research institute in a former USSR. They had a whole room with computers put in a Faraday cage to prevent any data leaks with supposedly secret information. The cage was a mesh made of thin metal sheets with 1mm holes. As I remember the whole thing was done seriously, not a fake to please some inspector. It had double doors, all cables were put into metal tubes, all lights were outside I suppose to minimize the cabling.
WalterBright 5y ago
> The question is, then, how well do they actually work? I tested some by putting the phone in the Faraday container, and then calling its number to see if it rang.
zanybear 5y ago
I can see a 99 dollars Faraday Cloth in the future
Ntrails 5y ago
Doesn't even try a crisp packet? Madness.
dsign 5y ago
Cheap science fiction book idea: imagine having to choose between living without your smartphone or living with every company and government agency willy-nilly spying on you. Oh, wait...
0xdeadb00f 5y ago
Wrapping your phone in aluminum foil also works. I've made a few DIY Faraday bags that way. They're not perfect of course, but less expensive than these bags most of the time. Edit: Ah, I see this was covered in the article. I didn't read it before posting this comment.
- taneq 5y ago
  It also keeps them from drying out when you microwave them while still maintaining a crispy skin.
  - Kaibeezy 5y ago
    Also, caution: If your phone is made from a tomato or other acidic substance, the foil may corrode, further reducing RF containment.
    - dotancohen 5y ago
      I believe that the Tomato is more commonly used for routers - this may be why! A good portion of phones, on the other hand, do seem to be made of the fruit of the domesticated Malus.
scottdupoy 5y ago
> While the cookie tin performed much better than the mylar bags, and could provide a modicum of useful attenuation under some circumstances, it was not sufficient to provide meaningful assurance of signal isolation at any frequency. However, it was unique among the containers tested in providing tasty snacks during measurements Back in the day working for Symbian I used to regularly have to run a load of automated Bluetooth tests. Unfortunately there were 200+ engineers in the close vicinity of my test setup and they all had smartphones and all had Bluetooth turned on, causing loads of the test to timeout. We were very pleased with ourselves when we thought of using a biscuit tin as a Faraday cage to try and improve things. Didn't work as well as we hoped, but got the tests running within their timeouts. I always thought it'd be interesting to try using an old microwave. Best thing was that we got to eat all the biscuits first :)
- Terry_Roll 5y ago
  How many different biscuit tins did you try? :-)
- kingcharles 5y ago
  When I was in jail I had a cellie who imported drugs from China. They were always shipped inside defunct microwave ovens. I wondered if it was just because it looked like a harmless kitchen appliance or because the microwave provided shielding from an x-ray scan?
  - habi 5y ago
    This really depends on the X-ray machine, a powerful x-ray source might easily penetrate a small appliance. A faraday cage/bag does not protect x-ray since it ‘only’ blocks electromagnetic fields. So I guess in the case you mention it’s more hiding in the insulation/empty space of an appliance.
    - BenjiWiebe 5y ago
      X-rays _are_ electromagnetic radiation.
bflesch 5y ago
Perfect timing, I was just looking up this topic in the last week. But how come these are all US-exclusive. It seems both winners don't ship to EU :/
jimmySixDOF 5y ago
My understanding is that a Faraday Cage, of any size, relies on a proper grounding system to work at all so these boxes and rfid blocking pockets etc all seem to be tinfoil hats parading as space age metamaterials.
- dtgriscom 5y ago
  Nope: RF shielding has nothing to do with having a ground reference.
- snowwrestler 5y ago
  A faraday cage converts the energy in the radio waves it absorbs into heat. Eventually it will radiate the same amount of energy as the transmitter inside it, but in infrared wavelengths and without whatever modulation was carrying the signal.
- formerly_proven 5y ago
  > relies on a proper grounding system to work at all does not
- h2odragon 5y ago
  Good RF ground is a bitch.
- authed 5y ago
  Apparently not: "Small Faraday cages with no conductors penetrating the shield do NOT need to be grounded."
noduerme 5y ago
Where I live, all I have to do to block 4G is to stop standing in the far corner of the yard.
- shapefrog 5y ago
  left arm not in the air and both feet on the ground seems to get rid of the 4g signal for me. I do miss the old days of tuning the rabbit ears on top of the tv for best reception.
  - Kaibeezy 5y ago
    Try this trick... with your feet in the air and your head on the ground, spin it. Did you get an earworm? I sure did.
djmips 5y ago
If you are sufficiently concerned, why not mod the phone to add a physical battery disconnect? Would this not provide 100% protection?
- catlikesshrimp 5y ago
  If you are concerned enough, but a phone with physical switches https://www.androidpolice.com/2020/08/22/this-smartphone-has-physical-kill-switches-for-its-cameras-microphone-data-bluetooth-and-wi-fi/ https://www.androidpolice.com/2020/08/22/this-smartphone-has... Or at least phone with a removable battery I know I will never buy a phone without a 3.5 audio jack
  - haarts 5y ago
    That last sentence surprises me a bit. What does a 3.5 audio jack have to with any of this?
    - catlikesshrimp 5y ago
      Manufacturers are always trying to push features that are more profitable to them. As expected. Non-removable batteries is the new standard because of that. (Also stream lining) Which is bad for security (the point of the article) I don't use bluetooth because it is not reliable enough for me, because I don't like charging another device and, less importantly, because in the past it has been exploited to hack devices. The audio jack is the one port I prefer never to part with.
- pdkl95 5y ago
  Even better: practice defense in depth and do both.
- bserge 5y ago
  Great idea! Kinda hard on glued smartphones, but still doable. Just need a switch between the + terminal and the rest of the phone, right? The more paranoid might think there's a backup battery somewhere, though.
- 5y ago
tgb 5y ago
Interesting results. The article states that Faraday cages are no directional. My physics 101 understanding of them was otherwise. You show they work by integrating over the surface of the cage and saying that's equal to the charge within the surface. But you don't say it's equal to the charge outside. Indeed it couldn't possible, since that charge could be light-years away and steady state would never be achieved. Now that was for electrostatic which isn't really what we care about, if I remember correctly. Wikipedia also states they are more effective at blocking incoming than outgoing signals. Can anyone clarify the situation?
- Johnythree 5y ago
  Building an effective Faraday Screen is surprisingly difficult: There are three completely different scenarios, blocking electrostatic fields, blocking RF energy, and blocking alternating magnetic fields. The first can be achieved by a thin conductive screen (eg brass mesh with soldered seams), the second by thick copper sheet (with bolted seams) and the third requires thick magnetic material (eg iron or nu-metal).
- pfortuny 5y ago
  If you consider the compactification of R^3 by a single point “at infinity”, an electric charge inside the surface is the same as the opposite charge at infinity (this is just Gauss’ result). In that sense, “infinity” acts as the opposite charge, does it not? I do not understand your question, otherwise. (Not a criticism, just an interested comment which may be very wrong though).
  - posix_me_less 5y ago
    > If you consider the compactification of R^3 by a single point “at infinity”, an electric charge inside the surface is the same as the opposite charge at infinity (this is just Gauss’ result) This is a mental operation, not physically possible. The difference is real: for example, charge inside a perfect conductor cavity generates electrostatic field outside. A charge outside perfect conductor cavity does not generate any static field inside.
ncmncm 5y ago
I wish it covered (so to speak) aluminum foil more thoroughly. In particular, foil is cheap, so rolling up in several layers (3? 5? 10?) and twisting the ends cracker-style ought to be more reliable and practical than trying to do it with one layer and fiddly seams. A suggested minimum number of layers and number of twists would be useful.
- stinos 5y ago
  I wish it had covered practical tests more thoroughly. As in: did the phone communication effectively drop dead once in the cages which measure well? Looks very likely based on those attenuation numbers, but still: 'question everything' is usually the way to go in test&measurement.
- rasz 5y ago
  I was hoping for this test https://www.youtube.com/watch?v=2u6KdHmoMbw https://www.youtube.com/watch?v=2u6KdHmoMbw
janekm 5y ago
The pink bag shown is actually a static dissipative bag, not a static shielding bag, so would not be expected to work. Though the article mentions trying other bags so no doubt some of those where static shielding (metallic appearance) bags. I've had a lot of fun in the past trying to shield Bluetooth devices for testing... metal filing cabinet? Practically no attenuation. Biscuit tin? Minimal attenuation like in the article. Modern radio receivers are ridiculously sensitive.
- deelowe 5y ago
  I noticed this as well. > "Makeshift Pouch 1: Electrostatic Mylar Bag" This is not a mylar bag. It's frustrating how often these two are confused, especially when said confusion can result in component damage.
jpl56 5y ago
Please reduce the image size, they seem to be 3 Mb each. Some people (especially if their phone is in a pouch) won't be able to get to the interesting parts of your article!
jmnicolas 5y ago
Interesting experiment however his experience with tinfoil and metal boxes doesn't match mine. I placed my phone wrapped in a towel inside a metal box: as soon as I close the lid I can't ping the phone on local WiFi and can't reach it with call (it goes direct to voicemail as if the phone was switched off). The GPS doesn't record any position while in the box. I didn't test the Bluetooth though. Same thing for my car keys inside a paper towel and aluminum foil: impossible to open the car even at touching distance. I wonder if he wrapped the device before putting it in the box or aluminum.
- mnw21cam 5y ago
  I would note that GPS is much more fragile than WiFi/Bluetooth/GSM. The GPS signals are already incredibly weak at the receiver.
pluc 5y ago
Surprised slnt.com isn't mentioned. Happy with their product.
motohagiography 5y ago
Glad to see these tested. I've been using the EDEC bags for probably a decade to have on hand for incident response/forensics in security consulting, but I never had the gear to test the bags, I just trusted their supplier. Good to know about millimeter wave / 5g though.
parkertomatoes 5y ago
I was hoping they would test chip bags, because it was a plot device in the most recent Terminator movie. After searching, I found that Kaspersky has a blog post on the topic: https://usa.kaspersky.com/blog/terminator-dark-fate-chips/18843/ https://usa.kaspersky.com/blog/terminator-dark-fate-chips/18... It surprised me that chip bags were more effective in their test than cookie tins, but only when they double-bagged it
- teddyh 5y ago
  Also used in the, IMHO, underappreciated film Enemy of the State (1998).
- alliao 5y ago
  truck drivers used them too to avoid tracking from their employer https://arstechnica.com/information-technology/2017/11/australian-man-uses-snack-bags-as-faraday-cage-to-block-tracking-by-employer/ https://arstechnica.com/information-technology/2017/11/austr...
intrasight 5y ago
I built something in college that needed UL testing for RF emissions, and visited a facility in Long Island with a TEMPEST room about the size of my house. Was very memorable. I also read an article this year by a guy that made his house radio-wave proof, because, he claimed, he was very sensitive to radio waves. It was WAY more involved than I would have guessed - for the same reasons discussed in this article and in this HN discussion. Nails and screws are a problem. Windows are a big problem. But still - how cool to be cut off from the onslaught of EM radiation.
lettergram 5y ago
I actually have a little cookie box, which is lined with heavy aluminum foil, which I put in a steel lunch box. Perhaps it sounds like overkill, but it’s the only way I seem to be able to fully isolate the devices. That said, I’d probably just buy a bag... but I’ve been trying to keep it with what I have lying around the house.
BongoMcCat 5y ago
> 20 dB represents a change of a factor of 10 in amplitude (volts), while 40 dB is a factor of 100, 60 dB a factor of 1000, and so on. I always thought it was 10dB, or one B that was a change of factor 10. Have I missed something?
- variaga 5y ago
  You're missing the distinction of power vs voltage. dB is defined in terms of power. Power is proportional to voltage squared. So a 10x increase in voltage == a 10^2 = 100x increase in power == a 20dB increase in power.
- js2 5y ago
  TIL: Two principal types of scaling of the decibel are in common use. When expressing a power ratio, it is defined as ten times the logarithm in base 10. That is, a change in power by a factor of 10 corresponds to a 10 dB change in level. When expressing root-power quantities, a change in amplitude by a factor of 10 corresponds to a 20 dB change in level. The decibel scales differ by a factor of two, so that the related power and root-power levels change by the same value in linear systems, where power is proportional to the square of amplitude. https://en.wikipedia.org/wiki/Decibel https://en.wikipedia.org/wiki/Decibel
yosito 5y ago
I'd be curious if anyone finds it worthwhile to have a smartphone while being so paranoid that you have to hide it in a Faraday bag. I understand the problem. I just don't understand the practical use case: every time you use the phone, you have to take it out of the Faraday bag, and it can be used to spy on you or report information about you. Assuming you're keeping it in the Faraday bag all day, when and why would you find it useful and worth the risk to take it out? And with that level of use, wouldn't it be more practical to have a dumb phone or a laptop?
- 24bug47 5y ago
  You would take out your phone if you would like to make a phone call, or check to see if you have received any messages. For the other 99% of your day, the IoT sensors being stuck on every conceivable object are unable to report back to HQ (and every agency and broker affiliated) your current whereabouts and trajectory.
  - yosito 5y ago
    So why not get a more basic phone and not a smart phone?
    - throwaway1777 5y ago
      Dumb phones still ping cell towers?
      - yosito 5y ago
        Sure, but they also have simpler hardware that's easier to audit and almost all have removable batteries, which is most likely just as effective as a faraday bag.
deleted 5y ago
[deleted]
gdelfino01 5y ago
Electronic voting machines should be put inside Faraday cages too. Specially now that communication chips have been found hidden in some of their motherboards. https://letsfixstuff.org/2021/04/modem-chips-embedded-in-voting-system-computer-motherboards/ https://letsfixstuff.org/2021/04/modem-chips-embedded-in-vot...
- effie 5y ago
  Electronic voting is much easier to subvert than boring old paper-tech voting. It should be rejected for important elections.
comeonseriously 5y ago
I think they could have done a better job with the aluminum foil. It looks rather not well done. He could have made a pouch and folded the sides over a few times. I made a pouch for my car's key fob with aluminum foil and metal tape. It isn't as pretty as the ones you can buy, but it wasn't $25 either and It has worked really well.
IncRnd 5y ago
This article was a fun read, and it really highlights how we trust the words on the tin to be accurate and not mistaken marketing gibberish. However, the part about the cost ranging from $40 - $80 is simply not true. I know this, because I purchased for $20 yesterday a faraday box to hold my auto key fobs and my cell phone. [1] There are very many items for sale at this price point, fabric, pouches and boxes. [1] https://smile.amazon.com/s?k=faraday+box https://smile.amazon.com/s?k=faraday+box
- pro_zac 5y ago
  Key fobs! Isn't there a scheme where thieves clone the signal from a key fob when the owner is asleep in their home and drive off with their car?
  - rrmoelker 5y ago
    The attack involves relaying the signal next to the car. Essentially mimicking the key fob being close to the car. For what I know you can not clone the key, nor can you record the signal and replay it whenever you want access. It's a one time thing to drive away to your nearest chop-shop/hideout.
  - IncRnd 5y ago
    Here's hoping I get a good faraday box from Amazon!
JohnJamesRambo 5y ago
That was really interesting. I can’t believe how poorly the metal tin box did compared to real faraday pouches.
- londons_explore 5y ago
  The metal tin box will have had varnish and paint on it's surfaces. That means at the junction between the tin and the lid (and maybe other joins), there isn't an electrical connection all along. Having two metal surfaces next to eachother, but with an insulator in between, acts like a 'choke flange'[1]. However, they only work at one specific frequency - at all other frequencies they will leak either a little signal or a lot/all the signal. The same technique is used on a microwave door edge to keep the microwaves in. It's why keeping the microwave door edge clean is critical to safety - a small bit of food there isn't an insulator like the paint, and energy leaks out. [1]: https://en.wikipedia.org/wiki/Waveguide_flange#Choke_connection https://en.wikipedia.org/wiki/Waveguide_flange#Choke_connect...
  - rubylark 5y ago
    That's interesting! As far as improvised faraday cages go, I always heard that microwave ovens are a good solution. Does this mean that microwave ovens wouldn't be any better as they would only block the specific microwave frequency they're designed for?
    - londons_explore 5y ago
      Correct. In fact, you can easily verify this by putting a phone in an unpowered microwave and calling it. It'll usually get both 4G (frequencies range, but 800Mhz in my area) and Wifi (over 5GHz).
  - op00to 5y ago
    TIL! Thanks!
  - coldacid 5y ago
    I wonder how many of us are going to end up cleaning our microwaves today after seeing this comment.
bborud 5y ago
At my former job we had a rather large faraday cage for testing telco equipment. Two things surprised me: 1) It is more fiddly to ensure a room-sized faraday cage doesn't leak RF than I thought. It is really easy to make mistakes that compromises experiments. 2) There was a bath-towel sized piece of cloth that came with one of the expensive Rohde & Schwarz instruments that was astonishingly effective at blocking signal. So I mainly used the room because that's where the magic blanket was - which was easier to use than ensuring the room was set up correctly.
- op00to 5y ago
  I see one of the founders (Ulrich Rhode) of Rhode and Schwarz on amateur radio some times, and I always ask for test equipment and he always says no.
  - relaxing 5y ago
    I once tried to acquire a RS PR100 like the one used in the test here. Turns out they cost more than a fancy car!
    - op00to 5y ago
      I wonder how much more capable they are than the cheap crap I can afford.
      - relaxing 5y ago
        A lot! An Ettus USRP + GNURadio could get you part of the way, but you then you don't get the nice handheld form factor and ruggedized chassis.
  - shapefrog 5y ago
    I see you are from <insert whatever company you are at is>, can you please send me a lifetime supply of whatever you make / have / sell please?
pdkl95 5y ago
I really like Snowden's recommended Faraday cage for phones or other devices of similar size: two drink-shaker cups[1]. Drink shakers are cheap and widely available. The average hotel room in any medium/large hotel chain probably includes a shaker as a standard item as part of the minibar. The simple two-cup style (as seen in [1]) is preferred over the fancier "strainer top" style because you can press the two cups together; this should cause the inner cup to slightly cut into and/or deform the outer cup along the circle where they join together. The seal between the cups should work sort of like the knife-edge seals used in vacuum chambers. A metal box or conductive bag is only a Faraday cage if it is fully closed/sealed. Any imperfection in the seal or hole[2] might allow the radio signal to leak out. Most improvised items (freezer, random metal box, etc) have poor seals. Making a high quality cage that actually block a modern phone can be done without much trouble, but the drink shaker method is the only method I know of that will do the job using widely available (free) or very cheap ($10-ish?) parts. [1] https://ae01.alicdn.com/kf/HLB1yRyhXZTxK1Rjy0Fgq6yovpXaZ/Wine-Cocktail-Shaker-Set-Mixing-Making-Drinking-Container-Barware-Bartender-Drink-Party-Bar-Tools-Stainless-Steel.jpg_Q90.jpg https://ae01.alicdn.com/kf/HLB1yRyhXZTxK1Rjy0Fgq6yovpXaZ/Win... [2] Holes of sufficient size. How big are the waves you are trying to block?
- kurthr 5y ago
  If you're interested in simple cages similar in effectiveness to the EDEC Window Pouch (they drop off above 3GHz)... try a Microwave Oven. They are highly available, reasonably convenient and well designed, with pretty good quality control. You can even still see your phone inside has zero bars. I do, however, recommend unplugging the microwave (or even cutting the power cord) as a fire would likely result from cooking your hardware. To answer [2] How big are the waves you're trying to block? - it's actually crack length not width that usually determines the effective re-radiating antenna length. They can be very narrow, but a long (a few cm) crack will allow one polarization through almost completely. I've run this test with a GSM base station and confirmed the effectiveness. If you want to test communication with a device to a base station, but have many other local antennas interfering and want to fit many devices inside... it's a decent choice. The alternatives are less convenient and usually thousands of dollars to construct.
whiw 5y ago
> Faraday cages are non-directional. Per-se, yes, agreed, but I was wondering whether the transmitter and receiver antenna couple into the surrounding screen differently. The degree of coupling may de-tune them differently. If so then the setup which most accurately represents the intended use would be with the receiver inside the screen.
tomxor 5y ago
> "Wrap it in tin foil" is perhaps the most common advice [...] Unfortunately the results were extremely inconsistent [...] 90 dB attenuation in one test would produce only 50 dB the next time [...] You would have no way to tell whether you've managed to fold and seal it adequately well On the other hand, aluminium foil is incredibly commonly available, if not in a kitchen draw, it will be at the nearest shop. Although unreliable, the _potentially_ high attenuation the author shared is pretty good (we don't know his worst reading), better than all other improvised solutions tested, and similar to commercial products. I wonder if a more reliable construction method could be found. I'm not sure what movie scene scenario I'm envisioning, but in the case you needed a Faraday cage and don't constantly carry one around, perhaps simply taking an entire kitchen roll of foil and wrapping the device into a giant unsightly ball of it would be a reliable enough process for an "emergency" (if not pocket sized). i.e rather than trying to make a neatly folded minimal version, just resort to sheer number of layers of material - unless RF doesn't care and even 1000 layers with tiny gaps is no good? [edit] Similarly, I wonder how well (or poorly) common household appliances work as a Faraday cage, e.g a fridge, microwave-oven - From what the author described, it seems they would all have too many gaps, however they are also constructed from higher gauge metals... i'm particularly interested in a microwave-oven which is specifically designed to reflect and retain microwave frequency fields.
- willis936 5y ago
  Microwave-ovens definitely don't leak below 2.4 GHz. Any frequency above that is a non-issue for microwave-oven operator safety. It also wouldn't be an issue for any communication device transmitting below 2.4 GHz. If you want to shut down 5 GHz communication then a microwave-oven would be leaky. 60 GHz: it shouldn't matter since it needs LoS anyway. Also, remember to ground your faraday cages.
  - posix_me_less 5y ago
    > ground your faraday cages. Why?
    - willis936 5y ago
SamuelAdams 5y ago
This is a super cool blog post. However I think it alludes to a much larger problem. For many products today, it’s very difficult or impossible for most people to verify the product works. For a network switch, there are free and open source tools like iPerf to test and verify speeds are as advertised. For a faraday box, you have to go through all these steps (and knowledge learned) just to be able to test these. What about for vitamins, or pet food, or any other “durable” products that are supposed to last for X years? In an age of snake oil salesmen, paid for reviewers, and fraudulent products on Amazon, there is a real opportunity for creating systems that enable individuals to verify products do what the sellers claim they do.
- RandallBrown 5y ago
  An easy solution would be putting your phone in the bag and have someone else call it. The post does mention something similar near the bottom where they suggest putting an AirTag in the bag and seeing if your phone can find it.
- throw10920 5y ago
  I'd like to describe a complementary problem to yours - that it's very difficult or impossible to find out others' experiences with a product's quality, durability, and performance. That is - the complement to the problem of "it's hard to determine if some products work" is "it's hard to find other users' experiences with the product". Amazon reviews are completely worthless, but very few other platforms have anywhere close to the same number of reviews on them. Most platforms have no verification of purchase for reviews. It's hard to determine information like "does this device require a cloud login? for which functionality? are there ads?" that isn't explicitly supplied by the manufacturer (or hidden by them). Negative reviews about product breaking quickly aren't very useful because people whose products work for a long time leave reviews at a lower rate. Google is almost useless for finding out information like this because of how SEO-gamed everything is, and the ol' "site:reddit.com" trick will only work for a while longer until these fraudsters create enough fake reviews on Reddit that it also succumbs (which is already beginning). (rant "...and this problem will likely won't be solved anytime soon, because consumers don't care about these things. That's the reason that we're in this situation - consumer apathy. When was the last time you heard a non-tech-savvy relative say something along the lines of "Wow, this phone didn't last very long. Is there a place where I can add that data point so that other people will be more informed before they purchase one?" Users don't care about performance, privacy, or durability - they just want to watch Netflix and pay the lowest sticker price they can (regardless of annual cost of ownership). You see people self-organizing around things like video games or paintball or book clubs or whatever all the time - why won't they put even a fraction of that effort into ensuring that they buy a good car?")
fsflover 5y ago
I prefer smartphones with kill switches, Librem 5 and Pinephone.
- 323 5y ago
  But you need to trust that they are actually working, and that the device was not intercepted and modified en route.
  - fsflover 5y ago
    They have the schematics [0,1] for these devices and even X-rays [1] for Librem 5. Also, anti-interdiction services for the latter [2]. [0] https://wiki.pine64.org/index.php/PinePhone#PinePhone_board_information.2C_schematics_and_certifications https://wiki.pine64.org/index.php/PinePhone#PinePhone_board_... [1] https://source.puri.sm/Librem5/community-wiki/-/wikis/Frequently-Asked-Questions#19-is-the-librem-5-freeopen-hardware https://source.puri.sm/Librem5/community-wiki/-/wikis/Freque... [2] https://puri.sm/posts/anti-interdiction-services/ https://puri.sm/posts/anti-interdiction-services/
    - effie 5y ago
      Isn't this rather a security theater for the more naive prospective buyers? Even if the device is verified to comply with high-level schematics, it still may not comply on the micro-level. There is the problem with all modem chips being able to access/control phone memory and being potentially controllable by the mobile network operator. How are we going to verify this vulnerability has been removed?
      - fsflover 5y ago
        If you want to go this deep, consider this: https://www.crowdsupply.com/sutajio-kosagi/precursor https://www.crowdsupply.com/sutajio-kosagi/precursor. See also: https://news.ycombinator.com/item?id=27897975 https://news.ycombinator.com/item?id=27897975.
pseudolus 5y ago
Bit of an aside but the ineffectiveness of tin foil hats to prevent government intrusion into our minds has been known for some time :) http://web.archive.org/web/20100708230258/http://people.csail.mit.edu/rahimi/helmet/ http://web.archive.org/web/20100708230258/http://people.csai...
- tzs 5y ago
  I've lately started seeing claims on some of the forums that embrace things like vaccines contain 5G mind control chips claiming that lead effectively blocks government mind control and that is the real reason lead paint was banned, and that it is not actually harmful.
  - Arrath 5y ago
    Oh for the love of god
- effie 5y ago
  Btw, to prevent abovementioned government/other powerful groups intrusions into our minds, I recommend to stop consuming MSM. That's the most powerful tool of intrusion/control they have.
f38zf5vdt 5y ago
If all phones were mandated to have a physically isolating means to disable their wireless chips, we could avoid this problem all together.
- 0xdeadb00f 5y ago
  Even then, how could you trust that the physical isolation switch is enough?
lmilcin 5y ago
That red plastic "mylar bag" isn't what should have been tested. Red plastic == electrostatic dissipative. It is not good at conducting electricity -- it is still very good insulator. It just has ability to dissipate electric charge fast enough so that it will not accumulate in normal use. What you have wanted to check is a clear bag with metalized layer (which is silver or gray looking). It should, per my understanding, act as much better faraday cage than an electrostatic dissipative bag. And I would be really interested in seeing that measurement.
deleted 5y ago
[deleted]
seanhunter 5y ago
One thing that most people should use a Faraday pouch for (in my opinion) is storing your key fobs if your vehicle uses keyless ignition with a fob. This prevents a very common relay attack which is to stand with a laptop by someone's front door and relay the keyfob signal between the keys (somewhere inside the person's house) and the car. For people who live in cities where you park on the street (as I do) it's extra-convenient for thieves in that most cars will flash some lights to say the alarm is disabled so the thieves know which car they just unlocked.
- skunkworker 5y ago
  I was also thinking about this, after seeing this reddit thread of a woman putting a device in front of a doorbell. https://www.reddit.com/r/whatisthisthing/comments/r7kb03/my_neighbors_shared_an_unsettling_video_of_a/ https://www.reddit.com/r/whatisthisthing/comments/r7kb03/my_...
  - seanhunter 5y ago
    Yeah a work colleague had his car stolen and his door cam recorded the thieves kind of waving a laptop about in front of it. I guess the antenna they use is highly directional so you have to get it just right to trigger. The apple watch unlock feature in recent macOs versions apparently avoids this relay attack by using a high-precision timer so they know (given the speed of light) that the watch is very close and the signal could not be relayed from a watch that's further away by a mitm (because the timestamp would be too old). I guess car keyfobs don't do this kind of thing because the electronics are intentionally quite primitive to avoid excessive battery drain.

368 points by jor-el 5y ago

What's the use case for these products? Even if the radio is blocked, how does that stop a device from collecting data anyway, and exfiltrating it the moment it finds a network? Won't it look for a network the moment you take it out of the bag? And don't you have to remove it from the bag to use it practically? Ultimately, if your device is compromised or untrustworthy to the extent that it has to be policed this way, is it not safer to just... get rid of it?

sanirank 5y ago
I still wonder why phone cases with physical blockers for camera and mic aren’t in high demand, and why there aren’t hundreds of pirated copies on the market for the ones that have been developed.

ziggus 5y ago

Solution: Wrap device in aluminum foil, place in Mylar bag, place bag in cookie tin.

docflabby 5y ago

Tinfoil hat on - has anyone considered how suspicious that only the commercial products worked, maybe the post is just a very clever shill for those products?

tablespoon 5y ago
> Tinfoil hat on - has anyone considered how suspicious that only the commercial products worked, maybe the post is just a very clever shill for those products? Not really, tinfoil actually worked, but it was apparently too difficult to get right: > In my experiments, I found I could sometimes achieve approximately 90 dB attenuation by carefully wrapping the generator in foil and double folding the seams on all sides, which is quite good (comparable to commercial pouches). This actually matches my experience with a GPS logger. It only had an on/off switch and I wanted to download the track from my trip without getting points from the download location at the end. IIRC, it was still able to get fixes even wrapped in tin foil.

aaroninsf 5y ago

I am happy to see EDEC performed well. Idle comment: we use their smaller keychain bags for car fobs, after hearing with dismay first- and second- hand accounts of relay attacks being used to steal or ransack cars in our neighborhood (94110). We now keep our fobs in them except in use.

Wistar 5y ago

Matt Blaze is a treasure.

wolverine876 5y ago

What is the use case for disabling wireless communication for your phone? How will you use it? How will anyone call you? If you don't want to use wireless functions, buy a tablet that lacks all the radio hardware.

jagged-chisel 5y ago
Bad Guys can't follow you using the signal. That's about it. Sure, they can tail you, but that's Work. And they'll know where you are the moment you take it out, but hopefully they're too far away to act on it. All in all, if you NEED something like this, your opec had better include more than this.
- wolverine876 5y ago
  > Bad Guys can't follow you using the signal. That's about it. Sure, they can tail you, but that's Work. And they'll know where you are the moment you take it out, but hopefully they're too far away to act on it. Why have the phone if it's not connected to the network? It's a communication device. Just leave the phone home.

_0w8t 5y ago

I visited at the end of eighties a research institute in a former USSR. They had a whole room with computers put in a Faraday cage to prevent any data leaks with supposedly secret information. The cage was a mesh made of thin metal sheets with 1mm holes. As I remember the whole thing was done seriously, not a fake to please some inspector. It had double doors, all cables were put into metal tubes, all lights were outside I suppose to minimize the cabling.

WalterBright 5y ago

> The question is, then, how well do they actually work? I tested some by putting the phone in the Faraday container, and then calling its number to see if it rang.

zanybear 5y ago

I can see a 99 dollars Faraday Cloth in the future

Ntrails 5y ago

Doesn't even try a crisp packet? Madness.

dsign 5y ago

Cheap science fiction book idea: imagine having to choose between living without your smartphone or living with every company and government agency willy-nilly spying on you. Oh, wait...

0xdeadb00f 5y ago

Wrapping your phone in aluminum foil also works. I've made a few DIY Faraday bags that way. They're not perfect of course, but less expensive than these bags most of the time. Edit: Ah, I see this was covered in the article. I didn't read it before posting this comment.

taneq 5y ago
It also keeps them from drying out when you microwave them while still maintaining a crispy skin.
- Kaibeezy 5y ago
  Also, caution: If your phone is made from a tomato or other acidic substance, the foil may corrode, further reducing RF containment.
  - dotancohen 5y ago
    I believe that the Tomato is more commonly used for routers - this may be why! A good portion of phones, on the other hand, do seem to be made of the fruit of the domesticated Malus.

scottdupoy 5y ago

> While the cookie tin performed much better than the mylar bags, and could provide a modicum of useful attenuation under some circumstances, it was not sufficient to provide meaningful assurance of signal isolation at any frequency. However, it was unique among the containers tested in providing tasty snacks during measurements Back in the day working for Symbian I used to regularly have to run a load of automated Bluetooth tests. Unfortunately there were 200+ engineers in the close vicinity of my test setup and they all had smartphones and all had Bluetooth turned on, causing loads of the test to timeout. We were very pleased with ourselves when we thought of using a biscuit tin as a Faraday cage to try and improve things. Didn't work as well as we hoped, but got the tests running within their timeouts. I always thought it'd be interesting to try using an old microwave. Best thing was that we got to eat all the biscuits first :)

Terry_Roll 5y ago
How many different biscuit tins did you try? :-)
kingcharles 5y ago
When I was in jail I had a cellie who imported drugs from China. They were always shipped inside defunct microwave ovens. I wondered if it was just because it looked like a harmless kitchen appliance or because the microwave provided shielding from an x-ray scan?
- habi 5y ago
  This really depends on the X-ray machine, a powerful x-ray source might easily penetrate a small appliance. A faraday cage/bag does not protect x-ray since it ‘only’ blocks electromagnetic fields. So I guess in the case you mention it’s more hiding in the insulation/empty space of an appliance.
  - BenjiWiebe 5y ago
    X-rays _are_ electromagnetic radiation.

bflesch 5y ago

Perfect timing, I was just looking up this topic in the last week. But how come these are all US-exclusive. It seems both winners don't ship to EU :/

jimmySixDOF 5y ago

My understanding is that a Faraday Cage, of any size, relies on a proper grounding system to work at all so these boxes and rfid blocking pockets etc all seem to be tinfoil hats parading as space age metamaterials.

dtgriscom 5y ago
Nope: RF shielding has nothing to do with having a ground reference.
snowwrestler 5y ago
A faraday cage converts the energy in the radio waves it absorbs into heat. Eventually it will radiate the same amount of energy as the transmitter inside it, but in infrared wavelengths and without whatever modulation was carrying the signal.
formerly_proven 5y ago
> relies on a proper grounding system to work at all does not
h2odragon 5y ago
Good RF ground is a bitch.
authed 5y ago
Apparently not: "Small Faraday cages with no conductors penetrating the shield do NOT need to be grounded."

noduerme 5y ago

Where I live, all I have to do to block 4G is to stop standing in the far corner of the yard.

shapefrog 5y ago
left arm not in the air and both feet on the ground seems to get rid of the 4g signal for me. I do miss the old days of tuning the rabbit ears on top of the tv for best reception.
- Kaibeezy 5y ago
  Try this trick... with your feet in the air and your head on the ground, spin it. Did you get an earworm? I sure did.

djmips 5y ago

If you are sufficiently concerned, why not mod the phone to add a physical battery disconnect? Would this not provide 100% protection?

catlikesshrimp 5y ago
If you are concerned enough, but a phone with physical switches https://www.androidpolice.com/2020/08/22/this-smartphone-has-physical-kill-switches-for-its-cameras-microphone-data-bluetooth-and-wi-fi/ https://www.androidpolice.com/2020/08/22/this-smartphone-has... Or at least phone with a removable battery I know I will never buy a phone without a 3.5 audio jack
- haarts 5y ago
  That last sentence surprises me a bit. What does a 3.5 audio jack have to with any of this?
  - catlikesshrimp 5y ago
    Manufacturers are always trying to push features that are more profitable to them. As expected. Non-removable batteries is the new standard because of that. (Also stream lining) Which is bad for security (the point of the article) I don't use bluetooth because it is not reliable enough for me, because I don't like charging another device and, less importantly, because in the past it has been exploited to hack devices. The audio jack is the one port I prefer never to part with.
pdkl95 5y ago
Even better: practice defense in depth and do both.
bserge 5y ago
Great idea! Kinda hard on glued smartphones, but still doable. Just need a switch between the + terminal and the rest of the phone, right? The more paranoid might think there's a backup battery somewhere, though.
5y ago

tgb 5y ago

Interesting results. The article states that Faraday cages are no directional. My physics 101 understanding of them was otherwise. You show they work by integrating over the surface of the cage and saying that's equal to the charge within the surface. But you don't say it's equal to the charge outside. Indeed it couldn't possible, since that charge could be light-years away and steady state would never be achieved. Now that was for electrostatic which isn't really what we care about, if I remember correctly. Wikipedia also states they are more effective at blocking incoming than outgoing signals. Can anyone clarify the situation?

Johnythree 5y ago
Building an effective Faraday Screen is surprisingly difficult: There are three completely different scenarios, blocking electrostatic fields, blocking RF energy, and blocking alternating magnetic fields. The first can be achieved by a thin conductive screen (eg brass mesh with soldered seams), the second by thick copper sheet (with bolted seams) and the third requires thick magnetic material (eg iron or nu-metal).
pfortuny 5y ago
If you consider the compactification of R^3 by a single point “at infinity”, an electric charge inside the surface is the same as the opposite charge at infinity (this is just Gauss’ result). In that sense, “infinity” acts as the opposite charge, does it not? I do not understand your question, otherwise. (Not a criticism, just an interested comment which may be very wrong though).
- posix_me_less 5y ago
  > If you consider the compactification of R^3 by a single point “at infinity”, an electric charge inside the surface is the same as the opposite charge at infinity (this is just Gauss’ result) This is a mental operation, not physically possible. The difference is real: for example, charge inside a perfect conductor cavity generates electrostatic field outside. A charge outside perfect conductor cavity does not generate any static field inside.

ncmncm 5y ago

I wish it covered (so to speak) aluminum foil more thoroughly. In particular, foil is cheap, so rolling up in several layers (3? 5? 10?) and twisting the ends cracker-style ought to be more reliable and practical than trying to do it with one layer and fiddly seams. A suggested minimum number of layers and number of twists would be useful.

stinos 5y ago
I wish it had covered practical tests more thoroughly. As in: did the phone communication effectively drop dead once in the cages which measure well? Looks very likely based on those attenuation numbers, but still: 'question everything' is usually the way to go in test&measurement.
rasz 5y ago
I was hoping for this test https://www.youtube.com/watch?v=2u6KdHmoMbw https://www.youtube.com/watch?v=2u6KdHmoMbw

janekm 5y ago

The pink bag shown is actually a static dissipative bag, not a static shielding bag, so would not be expected to work. Though the article mentions trying other bags so no doubt some of those where static shielding (metallic appearance) bags. I've had a lot of fun in the past trying to shield Bluetooth devices for testing... metal filing cabinet? Practically no attenuation. Biscuit tin? Minimal attenuation like in the article. Modern radio receivers are ridiculously sensitive.

deelowe 5y ago
I noticed this as well. > "Makeshift Pouch 1: Electrostatic Mylar Bag" This is not a mylar bag. It's frustrating how often these two are confused, especially when said confusion can result in component damage.

jpl56 5y ago

Please reduce the image size, they seem to be 3 Mb each. Some people (especially if their phone is in a pouch) won't be able to get to the interesting parts of your article!

jmnicolas 5y ago

Interesting experiment however his experience with tinfoil and metal boxes doesn't match mine. I placed my phone wrapped in a towel inside a metal box: as soon as I close the lid I can't ping the phone on local WiFi and can't reach it with call (it goes direct to voicemail as if the phone was switched off). The GPS doesn't record any position while in the box. I didn't test the Bluetooth though. Same thing for my car keys inside a paper towel and aluminum foil: impossible to open the car even at touching distance. I wonder if he wrapped the device before putting it in the box or aluminum.

mnw21cam 5y ago
I would note that GPS is much more fragile than WiFi/Bluetooth/GSM. The GPS signals are already incredibly weak at the receiver.

pluc 5y ago

Surprised slnt.com isn't mentioned. Happy with their product.

motohagiography 5y ago

Glad to see these tested. I've been using the EDEC bags for probably a decade to have on hand for incident response/forensics in security consulting, but I never had the gear to test the bags, I just trusted their supplier. Good to know about millimeter wave / 5g though.

parkertomatoes 5y ago

I was hoping they would test chip bags, because it was a plot device in the most recent Terminator movie. After searching, I found that Kaspersky has a blog post on the topic: https://usa.kaspersky.com/blog/terminator-dark-fate-chips/18843/ https://usa.kaspersky.com/blog/terminator-dark-fate-chips/18... It surprised me that chip bags were more effective in their test than cookie tins, but only when they double-bagged it

teddyh 5y ago
Also used in the, IMHO, underappreciated film Enemy of the State (1998).
alliao 5y ago
truck drivers used them too to avoid tracking from their employer https://arstechnica.com/information-technology/2017/11/australian-man-uses-snack-bags-as-faraday-cage-to-block-tracking-by-employer/ https://arstechnica.com/information-technology/2017/11/austr...

intrasight 5y ago

I built something in college that needed UL testing for RF emissions, and visited a facility in Long Island with a TEMPEST room about the size of my house. Was very memorable. I also read an article this year by a guy that made his house radio-wave proof, because, he claimed, he was very sensitive to radio waves. It was WAY more involved than I would have guessed - for the same reasons discussed in this article and in this HN discussion. Nails and screws are a problem. Windows are a big problem. But still - how cool to be cut off from the onslaught of EM radiation.

lettergram 5y ago

I actually have a little cookie box, which is lined with heavy aluminum foil, which I put in a steel lunch box. Perhaps it sounds like overkill, but it’s the only way I seem to be able to fully isolate the devices. That said, I’d probably just buy a bag... but I’ve been trying to keep it with what I have lying around the house.

BongoMcCat 5y ago

> 20 dB represents a change of a factor of 10 in amplitude (volts), while 40 dB is a factor of 100, 60 dB a factor of 1000, and so on. I always thought it was 10dB, or one B that was a change of factor 10. Have I missed something?

variaga 5y ago
You're missing the distinction of power vs voltage. dB is defined in terms of power. Power is proportional to voltage squared. So a 10x increase in voltage == a 10^2 = 100x increase in power == a 20dB increase in power.
js2 5y ago
TIL: Two principal types of scaling of the decibel are in common use. When expressing a power ratio, it is defined as ten times the logarithm in base 10. That is, a change in power by a factor of 10 corresponds to a 10 dB change in level. When expressing root-power quantities, a change in amplitude by a factor of 10 corresponds to a 20 dB change in level. The decibel scales differ by a factor of two, so that the related power and root-power levels change by the same value in linear systems, where power is proportional to the square of amplitude. https://en.wikipedia.org/wiki/Decibel https://en.wikipedia.org/wiki/Decibel

yosito 5y ago

I'd be curious if anyone finds it worthwhile to have a smartphone while being so paranoid that you have to hide it in a Faraday bag. I understand the problem. I just don't understand the practical use case: every time you use the phone, you have to take it out of the Faraday bag, and it can be used to spy on you or report information about you. Assuming you're keeping it in the Faraday bag all day, when and why would you find it useful and worth the risk to take it out? And with that level of use, wouldn't it be more practical to have a dumb phone or a laptop?

24bug47 5y ago
You would take out your phone if you would like to make a phone call, or check to see if you have received any messages. For the other 99% of your day, the IoT sensors being stuck on every conceivable object are unable to report back to HQ (and every agency and broker affiliated) your current whereabouts and trajectory.
- yosito 5y ago
  So why not get a more basic phone and not a smart phone?
  - throwaway1777 5y ago
    Dumb phones still ping cell towers?
    - yosito 5y ago
      Sure, but they also have simpler hardware that's easier to audit and almost all have removable batteries, which is most likely just as effective as a faraday bag.

deleted 5y ago

[deleted]

gdelfino01 5y ago

Electronic voting machines should be put inside Faraday cages too. Specially now that communication chips have been found hidden in some of their motherboards. https://letsfixstuff.org/2021/04/modem-chips-embedded-in-voting-system-computer-motherboards/ https://letsfixstuff.org/2021/04/modem-chips-embedded-in-vot...

effie 5y ago
Electronic voting is much easier to subvert than boring old paper-tech voting. It should be rejected for important elections.

comeonseriously 5y ago

I think they could have done a better job with the aluminum foil. It looks rather not well done. He could have made a pouch and folded the sides over a few times. I made a pouch for my car's key fob with aluminum foil and metal tape. It isn't as pretty as the ones you can buy, but it wasn't $25 either and It has worked really well.

IncRnd 5y ago

This article was a fun read, and it really highlights how we trust the words on the tin to be accurate and not mistaken marketing gibberish. However, the part about the cost ranging from $40 - $80 is simply not true. I know this, because I purchased for $20 yesterday a faraday box to hold my auto key fobs and my cell phone. [1] There are very many items for sale at this price point, fabric, pouches and boxes. [1] https://smile.amazon.com/s?k=faraday+box https://smile.amazon.com/s?k=faraday+box

pro_zac 5y ago
Key fobs! Isn't there a scheme where thieves clone the signal from a key fob when the owner is asleep in their home and drive off with their car?
- rrmoelker 5y ago
  The attack involves relaying the signal next to the car. Essentially mimicking the key fob being close to the car. For what I know you can not clone the key, nor can you record the signal and replay it whenever you want access. It's a one time thing to drive away to your nearest chop-shop/hideout.
- IncRnd 5y ago
  Here's hoping I get a good faraday box from Amazon!

JohnJamesRambo 5y ago

That was really interesting. I can’t believe how poorly the metal tin box did compared to real faraday pouches.

londons_explore 5y ago
The metal tin box will have had varnish and paint on it's surfaces. That means at the junction between the tin and the lid (and maybe other joins), there isn't an electrical connection all along. Having two metal surfaces next to eachother, but with an insulator in between, acts like a 'choke flange'[1]. However, they only work at one specific frequency - at all other frequencies they will leak either a little signal or a lot/all the signal. The same technique is used on a microwave door edge to keep the microwaves in. It's why keeping the microwave door edge clean is critical to safety - a small bit of food there isn't an insulator like the paint, and energy leaks out. [1]: https://en.wikipedia.org/wiki/Waveguide_flange#Choke_connection https://en.wikipedia.org/wiki/Waveguide_flange#Choke_connect...
- rubylark 5y ago
  That's interesting! As far as improvised faraday cages go, I always heard that microwave ovens are a good solution. Does this mean that microwave ovens wouldn't be any better as they would only block the specific microwave frequency they're designed for?
  - londons_explore 5y ago
    Correct. In fact, you can easily verify this by putting a phone in an unpowered microwave and calling it. It'll usually get both 4G (frequencies range, but 800Mhz in my area) and Wifi (over 5GHz).
- op00to 5y ago
  TIL! Thanks!
- coldacid 5y ago
  I wonder how many of us are going to end up cleaning our microwaves today after seeing this comment.

bborud 5y ago

At my former job we had a rather large faraday cage for testing telco equipment. Two things surprised me: 1) It is more fiddly to ensure a room-sized faraday cage doesn't leak RF than I thought. It is really easy to make mistakes that compromises experiments. 2) There was a bath-towel sized piece of cloth that came with one of the expensive Rohde & Schwarz instruments that was astonishingly effective at blocking signal. So I mainly used the room because that's where the magic blanket was - which was easier to use than ensuring the room was set up correctly.

op00to 5y ago
I see one of the founders (Ulrich Rhode) of Rhode and Schwarz on amateur radio some times, and I always ask for test equipment and he always says no.
- relaxing 5y ago
  I once tried to acquire a RS PR100 like the one used in the test here. Turns out they cost more than a fancy car!
  - op00to 5y ago
    I wonder how much more capable they are than the cheap crap I can afford.
    - relaxing 5y ago
      A lot! An Ettus USRP + GNURadio could get you part of the way, but you then you don't get the nice handheld form factor and ruggedized chassis.
- shapefrog 5y ago
  I see you are from <insert whatever company you are at is>, can you please send me a lifetime supply of whatever you make / have / sell please?

pdkl95 5y ago

I really like Snowden's recommended Faraday cage for phones or other devices of similar size: two drink-shaker cups[1]. Drink shakers are cheap and widely available. The average hotel room in any medium/large hotel chain probably includes a shaker as a standard item as part of the minibar. The simple two-cup style (as seen in [1]) is preferred over the fancier "strainer top" style because you can press the two cups together; this should cause the inner cup to slightly cut into and/or deform the outer cup along the circle where they join together. The seal between the cups should work sort of like the knife-edge seals used in vacuum chambers. A metal box or conductive bag is only a Faraday cage if it is fully closed/sealed. Any imperfection in the seal or hole[2] might allow the radio signal to leak out. Most improvised items (freezer, random metal box, etc) have poor seals. Making a high quality cage that actually block a modern phone can be done without much trouble, but the drink shaker method is the only method I know of that will do the job using widely available (free) or very cheap ($10-ish?) parts. [1] https://ae01.alicdn.com/kf/HLB1yRyhXZTxK1Rjy0Fgq6yovpXaZ/Wine-Cocktail-Shaker-Set-Mixing-Making-Drinking-Container-Barware-Bartender-Drink-Party-Bar-Tools-Stainless-Steel.jpg_Q90.jpg https://ae01.alicdn.com/kf/HLB1yRyhXZTxK1Rjy0Fgq6yovpXaZ/Win... [2] Holes of sufficient size. How big are the waves you are trying to block?

kurthr 5y ago
If you're interested in simple cages similar in effectiveness to the EDEC Window Pouch (they drop off above 3GHz)... try a Microwave Oven. They are highly available, reasonably convenient and well designed, with pretty good quality control. You can even still see your phone inside has zero bars. I do, however, recommend unplugging the microwave (or even cutting the power cord) as a fire would likely result from cooking your hardware. To answer [2] How big are the waves you're trying to block? - it's actually crack length not width that usually determines the effective re-radiating antenna length. They can be very narrow, but a long (a few cm) crack will allow one polarization through almost completely. I've run this test with a GSM base station and confirmed the effectiveness. If you want to test communication with a device to a base station, but have many other local antennas interfering and want to fit many devices inside... it's a decent choice. The alternatives are less convenient and usually thousands of dollars to construct.

whiw 5y ago

> Faraday cages are non-directional. Per-se, yes, agreed, but I was wondering whether the transmitter and receiver antenna couple into the surrounding screen differently. The degree of coupling may de-tune them differently. If so then the setup which most accurately represents the intended use would be with the receiver inside the screen.

tomxor 5y ago

> "Wrap it in tin foil" is perhaps the most common advice [...] Unfortunately the results were extremely inconsistent [...] 90 dB attenuation in one test would produce only 50 dB the next time [...] You would have no way to tell whether you've managed to fold and seal it adequately well On the other hand, aluminium foil is incredibly commonly available, if not in a kitchen draw, it will be at the nearest shop. Although unreliable, the _potentially_ high attenuation the author shared is pretty good (we don't know his worst reading), better than all other improvised solutions tested, and similar to commercial products. I wonder if a more reliable construction method could be found. I'm not sure what movie scene scenario I'm envisioning, but in the case you needed a Faraday cage and don't constantly carry one around, perhaps simply taking an entire kitchen roll of foil and wrapping the device into a giant unsightly ball of it would be a reliable enough process for an "emergency" (if not pocket sized). i.e rather than trying to make a neatly folded minimal version, just resort to sheer number of layers of material - unless RF doesn't care and even 1000 layers with tiny gaps is no good? [edit] Similarly, I wonder how well (or poorly) common household appliances work as a Faraday cage, e.g a fridge, microwave-oven - From what the author described, it seems they would all have too many gaps, however they are also constructed from higher gauge metals... i'm particularly interested in a microwave-oven which is specifically designed to reflect and retain microwave frequency fields.

willis936 5y ago
Microwave-ovens definitely don't leak below 2.4 GHz. Any frequency above that is a non-issue for microwave-oven operator safety. It also wouldn't be an issue for any communication device transmitting below 2.4 GHz. If you want to shut down 5 GHz communication then a microwave-oven would be leaky. 60 GHz: it shouldn't matter since it needs LoS anyway. Also, remember to ground your faraday cages.
- posix_me_less 5y ago
  > ground your faraday cages. Why?
  - willis936 5y ago

SamuelAdams 5y ago

This is a super cool blog post. However I think it alludes to a much larger problem. For many products today, it’s very difficult or impossible for most people to verify the product works. For a network switch, there are free and open source tools like iPerf to test and verify speeds are as advertised. For a faraday box, you have to go through all these steps (and knowledge learned) just to be able to test these. What about for vitamins, or pet food, or any other “durable” products that are supposed to last for X years? In an age of snake oil salesmen, paid for reviewers, and fraudulent products on Amazon, there is a real opportunity for creating systems that enable individuals to verify products do what the sellers claim they do.

RandallBrown 5y ago
An easy solution would be putting your phone in the bag and have someone else call it. The post does mention something similar near the bottom where they suggest putting an AirTag in the bag and seeing if your phone can find it.
throw10920 5y ago
I'd like to describe a complementary problem to yours - that it's very difficult or impossible to find out others' experiences with a product's quality, durability, and performance. That is - the complement to the problem of "it's hard to determine if some products work" is "it's hard to find other users' experiences with the product". Amazon reviews are completely worthless, but very few other platforms have anywhere close to the same number of reviews on them. Most platforms have no verification of purchase for reviews. It's hard to determine information like "does this device require a cloud login? for which functionality? are there ads?" that isn't explicitly supplied by the manufacturer (or hidden by them). Negative reviews about product breaking quickly aren't very useful because people whose products work for a long time leave reviews at a lower rate. Google is almost useless for finding out information like this because of how SEO-gamed everything is, and the ol' "site:reddit.com" trick will only work for a while longer until these fraudsters create enough fake reviews on Reddit that it also succumbs (which is already beginning). (rant "...and this problem will likely won't be solved anytime soon, because consumers don't care about these things. That's the reason that we're in this situation - consumer apathy. When was the last time you heard a non-tech-savvy relative say something along the lines of "Wow, this phone didn't last very long. Is there a place where I can add that data point so that other people will be more informed before they purchase one?" Users don't care about performance, privacy, or durability - they just want to watch Netflix and pay the lowest sticker price they can (regardless of annual cost of ownership). You see people self-organizing around things like video games or paintball or book clubs or whatever all the time - why won't they put even a fraction of that effort into ensuring that they buy a good car?")

fsflover 5y ago

I prefer smartphones with kill switches, Librem 5 and Pinephone.

323 5y ago
But you need to trust that they are actually working, and that the device was not intercepted and modified en route.
- fsflover 5y ago
  They have the schematics [0,1] for these devices and even X-rays [1] for Librem 5. Also, anti-interdiction services for the latter [2]. [0] https://wiki.pine64.org/index.php/PinePhone#PinePhone_board_information.2C_schematics_and_certifications https://wiki.pine64.org/index.php/PinePhone#PinePhone_board_... [1] https://source.puri.sm/Librem5/community-wiki/-/wikis/Frequently-Asked-Questions#19-is-the-librem-5-freeopen-hardware https://source.puri.sm/Librem5/community-wiki/-/wikis/Freque... [2] https://puri.sm/posts/anti-interdiction-services/ https://puri.sm/posts/anti-interdiction-services/
  - effie 5y ago
    Isn't this rather a security theater for the more naive prospective buyers? Even if the device is verified to comply with high-level schematics, it still may not comply on the micro-level. There is the problem with all modem chips being able to access/control phone memory and being potentially controllable by the mobile network operator. How are we going to verify this vulnerability has been removed?
    - fsflover 5y ago
      If you want to go this deep, consider this: https://www.crowdsupply.com/sutajio-kosagi/precursor https://www.crowdsupply.com/sutajio-kosagi/precursor. See also: https://news.ycombinator.com/item?id=27897975 https://news.ycombinator.com/item?id=27897975.

pseudolus 5y ago

Bit of an aside but the ineffectiveness of tin foil hats to prevent government intrusion into our minds has been known for some time :) http://web.archive.org/web/20100708230258/http://people.csail.mit.edu/rahimi/helmet/ http://web.archive.org/web/20100708230258/http://people.csai...

tzs 5y ago
I've lately started seeing claims on some of the forums that embrace things like vaccines contain 5G mind control chips claiming that lead effectively blocks government mind control and that is the real reason lead paint was banned, and that it is not actually harmful.
- Arrath 5y ago
  Oh for the love of god
effie 5y ago
Btw, to prevent abovementioned government/other powerful groups intrusions into our minds, I recommend to stop consuming MSM. That's the most powerful tool of intrusion/control they have.

f38zf5vdt 5y ago

If all phones were mandated to have a physically isolating means to disable their wireless chips, we could avoid this problem all together.

0xdeadb00f 5y ago
Even then, how could you trust that the physical isolation switch is enough?

lmilcin 5y ago

That red plastic "mylar bag" isn't what should have been tested. Red plastic == electrostatic dissipative. It is not good at conducting electricity -- it is still very good insulator. It just has ability to dissipate electric charge fast enough so that it will not accumulate in normal use. What you have wanted to check is a clear bag with metalized layer (which is silver or gray looking). It should, per my understanding, act as much better faraday cage than an electrostatic dissipative bag. And I would be really interested in seeing that measurement.

deleted 5y ago

[deleted]

seanhunter 5y ago

One thing that most people should use a Faraday pouch for (in my opinion) is storing your key fobs if your vehicle uses keyless ignition with a fob. This prevents a very common relay attack which is to stand with a laptop by someone's front door and relay the keyfob signal between the keys (somewhere inside the person's house) and the car. For people who live in cities where you park on the street (as I do) it's extra-convenient for thieves in that most cars will flash some lights to say the alarm is disabled so the thieves know which car they just unlocked.

skunkworker 5y ago
I was also thinking about this, after seeing this reddit thread of a woman putting a device in front of a doorbell. https://www.reddit.com/r/whatisthisthing/comments/r7kb03/my_neighbors_shared_an_unsettling_video_of_a/ https://www.reddit.com/r/whatisthisthing/comments/r7kb03/my_...
- seanhunter 5y ago
  Yeah a work colleague had his car stolen and his door cam recorded the thieves kind of waving a laptop about in front of it. I guess the antenna they use is highly directional so you have to get it just right to trigger. The apple watch unlock feature in recent macOs versions apparently avoids this relay attack by using a high-precision timer so they know (given the speed of light) that the watch is very close and the signal could not be relayed from a watch that's further away by a mitm (because the timestamp would be too old). I guess car keyfobs don't do this kind of thing because the electronics are intentionally quite primitive to avoid excessive battery drain.