Universal Security Instruments USI-3204-2P-3CC Photoelectric 120-Volt AC/DC Wired-In Smoke and Fire Alarm, 2-Pack The pack includes a separate large size 5-5/8-Inch mounting bracket, which attaches to any standard rectangular or octagon junction box and covers drywall cutouts. Optional tamper-resistant feature deters removal of alarm from bracket Interconnect up to 18 units, 12 smoke alarms maximum; when one alarm goes off all units sound their alarm. The alarm also includes an originating alarm feature: when smoke is detected the red LED flashes on the initiating smoke alarm Photoelectric technology is generally more effective at detecting slow, smoldering fires. The included dust cover is designed to protect the smoke alarm from paint, dust or other contaminants during construction or remodeling The alarm has a convenient silence feature, which allows you to temporarily override nuisance alarms. This is ideal for cooking fumes and fireplaces The battery pull-tab allows battery activation without removing the alarm from the mounting bracket--thus reducing installation time. The easy access front-load battery drawer makes battery replacement quick and convenient