The TC-10U Door Contact/Wireless Transmitter from Optex is a battery-powered transmitter that is compatible with the RC-10U/RC-20U Chime Boxes and RG-10U Single Relay Receiver. When used as a wireless transmitter and installed in the backbox of any battery-operated detector, extended detection range and wireless notification to your RC-20U chime box is achieved. It allows you to instantly monitor larger areas with minimal false alarms for an enhanced sense of protection. When used as a door contact, the TC-10U Transmitter will send a signal to the RC-20U receiver chime box. This gives the user a notification when the door is opened, and is suitable for high traffic areas around entrances where an above door sensor is not practical.