120V AC Smoke Alarm, With Battery, Fast Install, Better Performance, Reduces Nuisance Alarms, Easy To Install, Easy To Maintain & Quality Engineered For Years Of Virtually Maintenance-Free Service, Ionization Sensor Which Helps Detect Fast Flaming Fires That Consume Combustible Materials Rapidly, 120V AC Interconnectable, With Maximum 18 Compatible Devices, Alarm Can Be Interconnected With Up To 12 Other Compatible Smoke Alarms & 6 Compatible Devices Like Bells, Horns, Repeaters & Door Closers, If 1 Unit Triggers An Alarm, All Smoke Alarms In The Series Will Sound, Power Indicators Show Which Unit In The Series Initiated The Alarm.