The TC-10U is a battery-powered door / window contact and wireless transmitter for the RCTD-20U (Wireless 2000). When used as a wireless transmitter and installed in the backbox of any of OPTEXfts battery operated detectors, extended detection range and wireless notification to your RC-20U chime box is achieved. Instantly monitor larger areas with minimal false alarms for a greater sense of protection. When used as a door contact, the TC-10U will send a signal to the RC-20U receiver chime box. This gives the user a notification when the door is opened, and is perfect for high traffic areas around entrances where an above door sensor is not practical.