Door Knocker Sensor-Transmitter - CentralAlert - Serene Innovati

Detects the vibration on door-knocking with Door Knocker Sensor. It can also connect to your existing doorbell, door chimes, or door intercom provided there is an external connection. Simple to install with adjustable sensitivity to avoid false alarms 2.5mm Jack for direct connection to your existing doorbell/door chime.

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