Heath Zenith"s 35/M-C door chime is intended for hardwired installation, and may be used with one or two doors. It features two distinctive chimes, one for the back door and one for the front, so you"ll know which door to head to. Powered by a 16-volt AC transformer, sold separately (see Heath Zenith accessories #121AC-A and #122C-A).--Josh DettweilerWhat"s in the Box Chime, hardware kit