Eavesdropping devices are pieces of electronic equipment that allow the listener to intercept private communications. One of the most common types of eavesdropping devices in use today is the wireless transmitter which picks up sound via a hidden microphone and broadcasts it to a receiver using radio frequencies. These kinds of eavesdropping devices are relatively easy to uncover by conducting an rf detector sweep. However eavesdropping devices that do not emit radio waves are much more problematic to identify and eliminate.
Parabolic microphones, or unidirectional microphones, are eavesdropping devices that are designed to pick up sound in only one direction. Background noise is suppressed allowing the eavesdropping device to clearly capture and magnify faint conversations at distances of 100m or more away. Some parabolic eavesdropping devices can be attached to binoculars or feature inbuilt viewfinders so that the listener can both see and hear private communications in vivid detail from afar. Many eavesdropping devices like this also feature an output jack which can be attached to a recorder.
Laser microphones are technologically superior eavesdropping devices that can be used to secretly listen in on conversations at distances of up to a kilometer away. These eavesdropping devices can be trained on windows or other objects and work by using a laser beam to detect and decode vibrations caused by sound pressure waves. Laser microphones are extremely expensive, highly sophisticated professional eavesdropping devices that are generally used by government agencies rather than amateurs.
Body bugs are eavesdropping devices that can either be worn on the body or attached to a handbag or briefcase. These sorts of eavesdropping devices generally consist of a tiny microphone that is just a few millimeters in diameter attached to a minidisk recording device which can be hidden in pockets or inside bags.
Alternatively, wired microphones and recorders can be hidden in walls and ceilings and since these kinds of eavesdropping devices do not emit radio frequencies they are generally very difficult to detect. Where gaining access to the interior of a target’s premises to plant a hidden microphone is not a possibility, wall contact microphones may be used as eavesdropping devices. All the listener has to do is hold the contact up against a solid brick, concrete, wooden or metal wall or door, and this highly sensitive eavesdropping device will pick up and amplify sounds on the other side.
Be aware that the microphones in computers can also be remotely activated by certain programs and used as eavesdropping devices, as can those in cell phones and telephone handsets.
There are a number of countermeasures that can be used to foil eavesdropping devices, including audio scrambler white noise generators which inject noise into the environment and make it harder for microphones to pick up on conversations. If you believe you may be a target for illicit eavesdropping devices a common sense approach for keeping sensitive conversations private is to talk in person outside of the home, office or car. Go to a busy, noisy place that you do not normally frequent. Keep your voice low so that any eavesdropping devices which may be trained on you will have a tough time separating your conversation from the background noise, and be sure to pick a different venue for your next confidential exchange.