Listening devices are used to eavesdrop on conversations remotely. Usually small and easy to hide, listening devices are used by law enforcement as well as private individuals. Blocking a listening device is usually a matter of either distorting the sound input received by the device, sending another sound to mask it, or blocking the sound outright. Typically, sound jammers are used to neutralise nearby microphones.
Purchase an audio jammer. These devices are rather expensive, but can be relied upon to desensitise any hidden microphones within a given diameter. Small and discreet, audio jammers can easily be hidden themselves.
Place the audio jammer in the room where you suspect a listening device may be present. The sound jammer will generate a random masking sound. If you decide to hide the audio jammer, take care not to hide it in a way that blocks its signal -- the inside of a tissue box is a good place to hide the device
Test your audio jammer's effectiveness. Sound jammers have been proven effective against tape recorders, hard wired microphones, RF transmitters and shotgun microphones. However, for added peace of mind, use your own listening device in a room in which an audio jammer is present and listen to the recorded results to see if you understand them.