A contact microphone is a microphone that picks up structure-borne sound by contact with solid bodies.
The difference between contact microphones and other microphones is that contact microphones pick up sound vibrations from solid bodies and are largely insensitive to sound waves from the air. They are usually piezoelectric microphones used as acoustic probes or as pickups for acoustic instruments. Piezo elements serve as sensors for contact microphones.
In audio technology, contact microphones are often used as pickups for guitars to pick up the vibrations of the soundboard.