Not exactly a listening device, but I was in an AirBnb once. Every time I would open the door, I could hear a notification being played in the upstairs unit. It

Not exactly a listening device, but I was in an AirBnb once. Every time I would open the door, I could hear a notification being played in the upstairs unit. It wasn't the back door that caused the notification, but the actual door the apartment I was staying in. It was displeasing.