"The First Alert Dual Sensor Smoke & Fire Alarm utilizes both ionization and photoelectric smoke sensors for optimal performance. Provides optimal sensing of smoke particles produced in both flaming and smoldering fires. Intelligent sensing technology reduces non-emergency or nuisance alarms. Product Style Alarm, Batteries Required Yes, 2 AA, Senses Smoke and fire, Battery Included Yes, Includes 3 Dual sensor smoke alarms w/ batteries, user manuals. Uses dual sensors to protect against the most common household fires Reduces nuisance alarms Determines between non-threatening and true emergencies Single button silence/test mutes unwanted alarms Operates on 2 AA batteries included"