Includes a 9-Volt super heavy duty battery to power the alarm in the event of an AC power failure * The convenient front-load pull-out drawer provides fast and easy battery replacement * The alarm sounds with its loud 85 decibel horn and the red LED indicator flashes. A green LED light indicates AC power * The mounting plate attaches to the junction box and covers drywall cutouts for easy installation * Permanently installed semiconductor sensor means no annual replacement sensors are required