The Code 1-Hardwired Smoke and Carbon Monoxide Detector with Battery Backup is a hardwired smoke alarm and carbon monoxide detector combo. It connects to your home's wiring (120V AC power) and uses 2 AA batteries as a backup in case of power failures. The Code One smoke alarm uses a photoelectric sensor that detect visible fire particles associated with slow smoldering fires, as opposed to an ionization sensor, which can be better at detecting less-visible fire particles from fast flaming fires. Additionally, this Code One smoke and carbon monoxide alarm uses an electrochemical carbon monoxide sensor, which offers readings of carbon monoxide gas. When the unit senses a smoke or carbon monoxide hazard, an 85-decibel alarm will sound. When the unit is nearing its end of life, it will begin to chirp. In the case of nuisance or false alarms, the Hush feature temporarily silences the Code 1-smoke and carbon monoxide detector. Install a smoke detector and carbon monoxide detector on each level of your home and inside and outside each bedroom. UL Certified with a 10-year limited warranty. Meets requirements of UL 2034, UL217, NFPA72, The State of California Fire Marshal, NFPA 101, FHA, and HUD.