CentralAlert Door Chime/Knock Sensor
Attach the transmitter to your existing door chime or intercom door announcer for vibration detection. When someone rings your door bell, it detects the vibration of the chime or the intercom speaker and sends a wireless signal to trigger the CA-360. Or, you can attach the CA-DX to the inside surface of your door to detect someone knocking on your door.
Simple to install with adjustabloe sensitivity to avoid false alarms.
It can also be wired directly to an existing door chime (less than 24VAC) to be triggered by the electrical signal from the doorbell.
Operates on two alkaline batteries (included), Battery life up to 10 months.
One year warranty.