Serene Innovations CentralAlert CA-DXH Hanging Door Knock Sensor

The Door Knock Sensor with Door Hanger is part of the CentralAlert Notification System by Serene Innovations. It sends to the CentralAlert receiver to notify you when someone is knocking on the door. The CA-DX Door Knock Sensor is ideal for bedrooms or hotel rooms and is safe and secure since there is no part visible outside the door.

Features:

• 2.4GHz operating frequency
  
• Up to 210 ft operating range
  
• Uses 2 AA alkaline batteries (not included)
  
• Dimensions: 2.5" x 3.8" x 1"