Contact microphones, true to the name, work when in contact with another solid object that transmits sound. You’d have to shout pretty loudly into one to get it register your voice otherwise.

A contact microphone is a form of microphone that senses audio vibrations through contact with solid objects. Unlike normal air microphones, contact microphones are almost completely insensitive to air vibrations but transduce only structure-borne sound. Often used as acoustic leakage probes, they also enjoy wide usage by electroacoustic music artists experimenting with sound. Contact microphones can be used to amplify sound from acoustic musical instruments, to sense drum hits, for triggering electronic samples, and to record sound in challenging environments, such as underwater under high pressure.