Vibration Detector

This little circuit may act as a vibration-activated burglar alarm. The sensor, which may be secured unobtrusively to a door or a window, is a an inexpensive piezo buzzer. Piezo ceramic material deforms under application of voltage, but the reverse also applies, i.e., a piezo ceramic element will produce a voltage if it is deformed in any way, by acoustic waves (sound) or mechanical vibration.