Photoelectric sensor technology senses visible fire particles, associated with smoldering fires, while an electrochemical sensor senses carbon monoxide Smoke alarm operates on a 120V wired power source with a 10-year sealed lithium battery backup Voice Alarm & an 85-decibel alarm announces a hazard when detected: “Fire!” = smoke or fire, "Warning! Carbon Monoxide!", or "Replace Alarm" when the alarm has reached its end-of-life span Enables extension of coverage & protection without any need for additional wiring Ambient Light Sensing feature establishes a day/night cycle and prevents late-night battery chirps in dark conditions LED warning light indicators alert you to various statuses: a green light indicates the unit is in proper working operation, an amber light indicates an operating error, and a red light indicate smoke or fire Interconnection capability: allows you to connect up to 24 Kidde smoke, heat, or CO alarms, with the possibly it interconnect 6 strobe lights or relay modules UL listed with a 10-Year limited manufacturer warranty on the alarm only (not a battery performance claim). Warranty begins when the alarm is powered on. If that date is unknown, it should be assumed that replacement is needed.