The Kidde Smoke & Carbon Monoxide Detector, Lithium Battery Powered, Interconnect Combination Smoke & CO Alarm with Voice Alert, model P4010DCSCO-W, is powered on a 10-year, sealed, lithium battery to protect during a power failure. Using photoelectric sensing technology, the combination smoke alarm detects smoke, fire, & carbon monoxide gas and warns with alarm, LED lights, & voice technology. For CO detection, the alarm will sound with 4 fast beeps and "warning carbon monoxide". For smoke detection, the alarm will sound with 3 beeps with the announcement of "Fire". A red LED will flash in unison with the voice alarm that warns of fire, carbon monoxide, & low battery. The Smart Hush feature silences the fire alarm for approximately 8 minutes. A maximum of 24 Kidde devices can be interconnected in a multiple station arrangement, but cannot exceed the NFPA (National Fire Protection Association) limit of 18 initiation devices, of which 12 can be smoke alarms. With 18 initiating devices (smoke, heat, CO, etc.), interconnected, it is still possible to interconnect 6 strobe lights and or relay modules. UL Certified with a 10-year limited warranty. Meets requirements of UL 2034, UL217, NFPA72, The State of California Fire Marshall, NFPA 101, FHA, & HUD.