The Gentex 7139CSC is a photoelectric single or multiple station smoke alarm. It's designed for 120V hardwired use and features a 9V battery backup for ensured safety even when power is lost. This Gentex hearing impaired smoke alarm features a temporal 3 (T3) audible signal for evacuation, as well as an ADA compliant 177 candela strobe light. This model uses photoelectric sensing technology to detect dangerous smoke conditions. This Gentex smoke alarm should be ceiling mounted and includes Form C relay contacts for remote annunciation.