From warmfuzzy@700:100/0 to All on Fri May 4 19:57:43 2018
A not-so-common method of detecting surveillance that transmits on radio frequency waves though the air is to get a meter that detects ultra-sound
noise (that spectrum of the sound that is above the normal audible spectrum. When the radio waves bounce around on windows or other things that have the right reflective properties a small amount of sound waves are produced as a result of the radio waves... so some people that say they can hear an
annoying high-pitch noise may actually, in reality, be hearing sound in a higher frequency than the rest of us. A good way to verify if one can
actually "hear" radio-waves is to go into a TEMPEST enclosure and see if the noise stops. It is not known by me if different modulations cause different noises, but I'd expect some sort of difference from WiFi as compaared with FM radio.