Universal Security Instruments CD-9390 120-Volt AC/DC Wired-In 3-LED Interconnectable Carbon Monoxide Alarm 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