BRK Electronics First Alert 4120B 120V AC/DC Hardwired with 9V Battery Backup Ionization Smoke Alarm (Upgraded to SMI100-AC)

BRK 4120B Smoke Alarm AC Powered with Battery Back-up. Designed for the fastest possible installation! If AC power fails, the battery back-up keeps the smoke alarm working. Ionization Sensor Quick Plug-In Power Connector Alarm Indication Battery Drawer Lock Mounting Bracket Lock Swing-Open Battery Door Battery Activation Tab Battery Back-Up AC Power Indicator Low Battery Warning "Chirp" Missing Battery Tab 9V Battery Included 10-Year Limited Warranty On Alarm Model # 4120B Operating Voltage 120V AC 60Hz w/ 9V battery backup (4120B only) Interconnections Up to 11 additional BRK smoke detectors and 6 compatible devices such as bell, repeaters, or switches. Listing UL Listed to U.S. and Canadian safety standards