CentralAlert Door Knock Sensor Model CA-DX

Install device on existing door chime or intercom door announcer for vibration detection. When someone rings your door bell, it detects vibration and sends a wireless signal to trigger the CA-360 to alert. Or, you can attach the CA-DX to the inside surface of your door to detect the knocking on your door. Product Features:  Detects vibration form existing doorbell or door chime and sends signal to CA-360 when someone is at the door Attach to or place near existing doorbell or door intercom 2.5mm jack for direct connection to doorbell terminal Optional door-knob hanger for hotel kit Sensitivity adjustment