Listening through the wall makes a fun children's game for siblings with rooms that share a wall. Sometimes children try to listen through a wall to eavesdrop on their parents' discussion about potential punishments for misdeeds. Practical applications include finding evidence of vermin or water leakage within a wall. However, eavesdropping presents legal and ethical issues. Listening through a neighbour's or stranger's wall may constitute a breach of their rights to privacy, which could make you liable to being sued in civil court.
Use a drinking glass to listen through the walls. Children have used this method to spy on family members for decades. This simple and cheap method offers moderate hearing ability. It works better with drywall than plaster and will not work with brick or concrete walls. Place the rim of the glass on the wall. Put your ear to the bottom of the glass and listen. A thin glass works better than glasses with thick bottoms. Any sound in the listener's room will distract the ear and limit hearing ability.
Put your ear to the wall. If the walls are thin, simply putting your ear to the wall will afford some listening opportunities. Walls made of drywall without insulation work best. Plaster blocks more sound. To effectively hear anything you will have to press the side of your head against the wall. Holding this position for an extended period of time may uncomfortable.
Use a listening device made specifically to listen through walls. Such devices use a microphone attachment to amplify the sounds coming from the other side of the wall. They can pick up sounds from behind walls built from almost any material. Use headphones for better listening. This listening device detects sounds within the walls such as pipe leaks. Because it can pick up sounds within concrete, it helps locate water leaks in concrete foundations. Most of these devices include recording capabilities. Recording people without their permission may pose both criminal and civil legal problems.
The room that the listener is in must be completely quiet.