Radios make the inaudible audible. Unlike ordinary microphones and amplifiers, which make very quiet acoustic sounds much louder, radios pick up electromagnetic waves that have no acoustic presence whatsoever and translate them into electronic signals that can be amplified and heard through a loudspeaker. An alternate approach to picking up electromagnetic signals is to use a simple coil of wire and an amplifier. In addition to constituting the basic mechanism of radios, microphones, and speakers, electromagnetic fields have spookier aspects that have been central to instrument design and artists’ works for nigh on 100 years. Toward the end of the 1970s, German sound artist Christina Kubisch began using electromagnetic induction to transmit local sound fields that followed wires she arranged around rooms to form “sound labyrinths,” heard over specially designed receivers, often embedded in headphones. In the process of receiving and demodulating transmissions, radios in turn generate and send back out intermediary electromagnetic signals.