Usually, the exposure limit is based on an active phone next to an ear. RF field strength falls off with the square of distance, so a phone on each side of your

Usually, the exposure limit is based on an active phone next to an ear. RF field strength falls off with the square of distance, so a phone on each side of your head is most dangerous to the respective ear and bits of your brain close to your skull; each phone is considered acceptably safe to the middle of your brain and the opposite ear.