This ultra sensitive wide-band E-smog detector offers you two extra senses to track down noise that’s normally inaudible. TAPIR – short for Totally Archaic but Practical Interceptor of Radiation – also makes a nice project to build: the kit comprises everything you need — even the enclosure, ingeniously consisting of the PCB proper.
Using the TAPIR is dead easy. Connect the headphones and an antenna and switch it on. Move it around any electrical device and you’ll hear different noises with each device, depending on the type and frequency of the emitted field.