The Kidde Smoke Detector, Hardwired with Smart Features and Voice Alerts, model P4010ACS-WF, is a hardwired smoke alarm that uses photoelectric sensor technology to detect visible fire particles, associated with slow smoldering fires. In the event of smoke, an 85-decibel alarm will sound and a voice alert will announce, Fire. The Kidde smoke alarm connects to your home’s wiring through 120-Volt AC power and has a lithium battery backup in case of power failure, providing continuous protection throughout the 10-year life of the alarm with the benefit of never having to change a battery. When the unit needs to be replaced, the alarm will announce Replace alarm. Provides real-time detection information and provides a means to set up alerts for family and friends – even the pet sitter – to alert to a potentially dangerous situation in your home. An LED ring-light indicator alerts you to the various state of the alarm: green equal normal operation, amber equal operating error and red = a smoke or fire hazard. A Test-Hush button temporarily silences nuisance alarms and tests the unit. Capable of whole-home activation with select Kidde alarms that have hardwired AC interconnect capability (see User Guide), so when 1 alarm sounds, they all do. Install a smoke detector on each level of your home and inside and outside each bedroom. UL Certified.