This door switch is triggered when the is opened. The sensor sends a wireless radio signal to the indoor receiver display (up to 1000 feet away) which will chime and flash letting you know the mail has arrived. If the supervised transmitter is removed , stolen, loses signal or battery is low, the receiver will produce a single beep once a minute. Sensor uses one 3 volt lithium battery (included), with an average life of 5 years in normal use. Receiver uses 120 VAC input/12VDC output adapter (included).
