Ensure the safety of your loved ones with the First Alert(R) 120 V hardwired smoke alarm equipped with a 9 V battery backup in case of power failure. The alarm comes equipped with an ultra-reliable ionization sensor to provide the earliest possible warning of a fast-flaming fire. The unit features an alarm indicator that automatically identifies which unit, in an interconnected series, initiated the alarm. It also comports a battery compartment and alarm base locking mechanisms and a single test/silence button. This product is backed by a 10-year limited warranty.