Hardwired smoke and carbon monoxide alarm. Interconnectable with AA battery backup. Helps protect you and your family from two hazards - fire and potentially deadly carbon monixed in one device. This combination 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. 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. Ionization sensing alarms may detect invisible fire particles (associated with fast flaming fires) sooner than photoelectric alarms. Photoelectric sensing alarms may detect visible fire particles (associated with slow smoldering fires) sooner than ionization alarms. One-touch button - performs the following functions: Activates the Hush feature to temporarily silence nuisance alarms, tests the unit's electronics and verifies proper operation, silences a low battery chirp for up to 24 hours at a time for a maximum of 7 days, silences the end of life chirps for 24 hours at a time for a maximum of 7 days, resets the device during a CO alarm (Unit will re-enter alarm within 6 minutes of reset if 70 ppm or more of CO is present).