Universal Security Instruments USI-1103 120-Volt AC/DC Wired-In Ionization Smoke and Fire Alarm with Silence Feature and Lithium Battery Back-Up Interconnect up to 18 units, 12 smoke alarms maximum; when one alarm goes off all units sound their alarm Battery pull-tab reduces installation time; quick connect wiring harness allows for fast and easy installation State-of-the-art lithium technology keeps your life-saving alarm energized for a full 10-Year. Battery contains no toxic metals Ideal for new installations or replacement of most existing smoke alarms Full-size plastic dust cover can be used during painting or remodeling project to protect alarm from damage or containments