Hardwire Photoelectric, Smoke Alarm. Photoelectric Technology: Better at detecting slow smouldering, fires. 120V AC Direct-Wire – Interconnects with up to 24 units, of, which 18 can be initiating. 9V Battery Backup (included) – Continuous protection in case, of power failure. Test Button – Tests circuitry and verifies alarm operation. Low Battery Indicator – Warning chirp sounds when battery, needs replacement. Interconnectable – ANY unit that senses a problem automatically, triggers ALL units throughout the home immediately, allowing, extra time for escape., Product dimensions: 6 x 6 x 1.5 deep, Colour / Case Pack: White / 6 units, Electrical Rating: 120V AC, 60Hz, 60mA, 9V Battery Backup, Wiring: Quick connect plug with 8 pigtails, Audio Alarm: 85dB, Temperature Range: 40ºF (4.4ºC) to 100ºF (37.8ºC), Humidity Range: Up to 85% relative humidity, Sensor: Photoelectric, Weight: 0.45lb