China Wholesale Door Bell

A doorbell is a signaling device commonly found near a door. It commonly emits a ringing sound to alert the occupant of the building to a visitor's presence. In most wired systems, a button, located around the height of the doorknob, activates a signaling device (usually a chime, bell, alarm or buzzer) inside the building. This single-pole, single-throw (SPST) switch momentarily closes the doorbells circuit. One terminal of this button is wired to a terminal on a transformer. A doorbell transformer steps down the 120-240volt AC electrical power to a lower voltage, typically 10-20 volts. Then transformer other terminal connects to one of three terminals on the signaling device. Another terminal is connected to a wire that travels to the other terminal on the button. If there is another button (typically near a back door), it is connected between the transformer and the third terminal on the signaling device. Unfortunately, the transformer, being energized constantly, consumes a small amount (about 1 to 2 W) of standby power constantly.