The RC-20U is the reciever / chime for the RCTD-20U (Wireless 2000). The device is powered by a AC adaptor (included), and up to nine TD-20U's can be added to one RC-20U receiver. (With an additional three added to a latching zone) In addition, the RC-20U includes a Form-C relay for activating additional devices such as lights, a camera, door lock, ect.
***Products are backwards compatible and will work with the TC-10U & TD-10U Series***