Replacement Door Knock Transmitter
Know when someone knocks at the door! The Door Knock Transmitter with Clip is a replacement or an accessory transmitter to expand your Clarity Alertmaster notification system.
The transmitter sends a signal to a connected Clarity Alertmaster receiver (not included), which then notifies you of the door knock with a visual or vibrating alert.
Easy to Install: Simply clip the transmitter to the inside face of the door using the included clip and flip the power switch on. Knocking on the door will activate the unit.
More information: http://www.hearmore.com/store/prodView.asp?idproduct=12086&idstore=6&product=Replacement-Door-Knock-Transmitter