First Alert SADUAL Dual Sensor Smoke and Fire Alarm (Model SA320) utilizes both ionization and photoelectric smoke sensors for optimal performance - detects both fast flaming and slow smoldering fires. Smart sensing technology helps recognize the difference between non-threatening conditions and real emergencies. Mute bottom serves purpose of quickly silencing alarm and testing it's function. Powered by 2-AA batteries (included) with EZ access battery door - allows you to change batteries without removing the alarm from the ceiling. Meets UL217 standards and backed by 10 year warranty.