Serene CentralAlert Accessory - CADXH Wireless Door Knock Sensor Transmitter

Hang it on your doorknob to detect the knocking on your door. The CADXH sensor sends a wireless signal to trigger the CA360 to alert you that someone is at the door. Ideal for both home and hotel stay applications.

Features:

• Detect vibrations from knocks on the door.
• 2.4GHz operating frequency
  
• Up to 210 ft operating range
  
• Uses 2 AA alkaline batteries (not included)
  
• Battery Life: Up to 10 months
• Dimensions: 2.5" x 3.8" x 1"
• Net Weight: 4 Oz