A contact microphone is a kind of transducer 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 (source: Wikipedia).
My contact microphone is entirely DIY and is based on the Alex Rice priezo preamp
as described by Zach Poff.
I've done the PCB routing using eagle and I've etched it using UV method.