First Alert 3120B Hardwire Photoelectric and Ionization Smoke Alarm with Battery Backup (2 Pack) Dual Photoelectric and Ionization sensing technologies for optimal sensing of smoke particles produced in both flaming and smoldering fires Two Latching Features Optipath 360 Technology Single button silence/test, and loud 85dB alarm 2 AA Batteries Included; 10 Year Limited Warranty