Ultra-sonic noise injected into vulnerable areas will nullify any type of microphone. In the case of contact mics, the noise will cause the surface with the attached microphone to vibrate, stopping it from picking up the much more delicate vibrations caused by room audio. In the case of free microphones, the noise will cover the sound of speach, . There are several purpose-designed devices designed to create such audio masks. Similar methods may be obtained much more cheaply by placing speakers against a suspect room, provided that whatever the speakers are outputting is as close to random as possible, to prevent the use of a DSP filter (Mexican radio stations are recomended).
Windows may be vibrated with the use of personal radios.
Free-space jamming is the process of flooding the medium that a surveillance device would be using to transmit on.