The PK-20A25WQ is a Piezo Transducer with wire termination. Piezoelectric electronic audible alarms work by converting the user input voltage to an appropriate oscillating signal that is applied to a sounder element that is mounted in housing. The piezoelectric sounder element consists of a metal disc that has a special ceramic material bonded to it that physically bends when voltage is applied to it. By applying a sinusoidal waveform at an appropriate frequency, the transducer will physically deflect in one direction and then in the opposite direction following the shape of the input wave-form. If this oscillation occurs in the audible frequency range (1Hz to 20kHz), then air pressure waves are produced that the human ear interprets as an audible sound. The larger the voltage of the applied wave-form, the larger the amplitude of the air pressure waves resulting in a louder sound level.