A cheap AM radio and inductive coil can eavesdrop on hidden electromagnetic signals in everyday electronics

Consumer AM radios pick up electromagnetic radiation emitted as a byproduct by computers, motors, fluorescent lights, camera flashes, and similar devices. Tuning the radio to a dead band converts these stray signals into audible sound. A telephone tap coil (or loose guitar pickup) plugged into an amplifier acts as a low-frequency stethoscope, letting the performer map a circuit board’s sound by moving the coil over components. Single-coil guitar pickups capture more electromagnetic garbage than humbuckers. Moving the coil near the amplifier’s speaker creates Theremin-like smooth feedback. The technique was pioneered by artists including Jerome Noetinger and Andy Keep.

Examples

Hold an AM radio near a laptop; tune to a dead spot and sweep the band as you move over the CPU vs. RAM vs. disk drive. Pass a telephone tap coil over a neon sign or fluorescent fixture.

Assessment

Explain why an AM radio tuned to a gap between stations picks up computer noise, and predict whether a humbucker or single-coil pickup would be more useful for this purpose.