You are Buying a brand New And Factory Sealed Kidde 10 Year Worry-Free Sealed Battery Combination Smoke and Carbon Monoxide Detector with Wire-Free Interconnect..... LED ring helps users quickly determine standby, alarm, or error mode of the alarm. Kidde P4010 Series Alarms contain 10-year tamper proof batteries that eliminate the need for battery replacement, and ends worry over unauthorized removal. Users are further shielded from late night battery chirps by the unit's Ambient Light Sensing feature, which establishes a day/night cycle and prevents alarm chirping in dark conditions. Wire-Free Interconnect triggers each connected alarm in the home to sound once smoke is detected, which can provide more time to react. The National Fire Alarm and Signaling Code (NFPA 72) has required smoke alarms in new homes to be interconnected since 1989, which traditionally involves running wiring to each alarm. Older and remodeled homes can now be updated to current standards without having to run any wiring to each alarm through walls and ceilings. Existing networks of interconnected alarms can be expanded with use of a single AC Wire-Free Alarm and additional compatible DC Wire-Free alarms.