First Alert SMOKE1000-AC-3 Atom Micro Photoelectric Smoke Alarm, Antique Copper, 3-Pack Award winning advanced micro design is 62% smaller diameter than a standard fire alarm - for maximum protection with a small footprint Photoelectric smoke sensor is resistant to nuisance alarms Includes long life 3V CR2 lithium battery and features a loud 85dB siren along with a test/silence button SmartClipTM safe mounting system prevents alarm installation without battery Tested to the highest industry standards, meets UL safety standards