First AlertFirst Alert Atom Micro Photoelectric Smoke and Fire Alarm N/A Imported Advanced Micro Design 62% Smaller Than Typical Smoke Detector Photoelectric Smoke Sensor Is Resistant To Nuisance Alarms Features Loud 85db Siren & Test/silence Button Smart clip Safe Mounting System Prevents Alarm Installation Without Battery Advanced micro design is 62% smaller diameter than a standard alarm - for maximum protection with a small footprint Photoelectric smoke sensor is resistant to nuisance alarms Includes long life 3V CR2 lithium battery Features loud 85dB siren and single test/silence button SmartClipTM safe mounting system prevents alarm installation without battery