Worry-free smoke alarm provides serious protection, with a sealed-in lithium battery that operates continuously for ten years and provides alert when it is time to replace. Contains photoelectric sensor with Smart Hush? feature that may detect small visible particles associated with smoldering fires earlier than ionization alarms. Self-activates when attached to mounting bracket. Red LED indicator light flashes when alarm has sounded. Test button evaluates integrity of alarm circuitry and activates Hush? feature. With talking voice alarm that announces: "Fire! Fire!". Power Source(s): Lithium-Ion Battery; Mounting: Universal Mounting Bracket.