A contact microphone is a type of microphone that picks up sound through the vibration of solid surfaces, rather than picking up sound waves from the air.

Think of it as a stethoscope for instruments. You attach it directly to the surface of an object (like the top of a guitar or the skin of a drum). It then converts the mechanical vibrations of that surface into an electrical signal.

Because it doesn't have a diaphragm that reacts to air, it's excellent at isolating the sound from the instrument, being very resistant to feedback and leakage of other ambient sounds.

It's a popular solution for amplifying acoustic instruments on noisy stages. It's also known by the slang term "Bug".