This First Alert® unit is a 120 V AC powered hard wired combination photoelectric smoke and carbon monoxide alarm with battery backup. It is equipped with a rapid connect feature for an easy installation. It features photoelectric smoke detection and electromechanical carbon monoxide detection as well as 85 dB siren at 10'. It gives you an end-of-life signal telling when the unit needs to be replaced and 2 silence functions, to silence low battery indicator for 8 hours or to temporarily silence a false alarm. A maximum of 18 detectors can be connected, 12 of which can be smoke alarms. The technology OptiPath 360 is a patented design providing unobstructed 360° access to the smoke detector. The tamper-resistant locking pin makes it ideal for rental units. This product is backed by a 10-year limited warranty.