The Hardwired Smoke & Carbon Monoxide Voice Alarm, Interconnectable with AA Battery Backup helps protect you and your family from two hazards – fire and potentially deadly CO – in one device. This smoke & carbon monoxide combo alarm features self-testing components that are always checking to make sure the alarm is on and working.* Additionally, the included mounting bracket makes installation fast and easy. This smoke and CO alarm is capable of being hardwired to other select Kidde alarms,** to provide whole-home alarm activation. This setup allows select Kidde alarms to sound in unison, helping to ensure that everyone in the house is alerted. Leading authorities recommend that both ionization and photoelectric smoke alarms be installed to help ensure optimal detection of the various types of fires that can occur within the home. Ionization sensing alarms may detect invisible fire particles (associated with fast flaming fires) sooner than photoelectric alarms. Photoelectric sensing alarms can detect visible fire particles (associated with slow smoldering fires) sooner than ionization alarms.