The Kidde Smoke Detector, 10-Year Battery, Photoelectric Sensor Wire-Free Interconnect Alarm, Voice Alert, model p4010DCS-W, uses photoelectric sensor technology to detect visible fire particles (associated with smoldering fires). When smoke or fire is detected, an 85-decibel alarm will sound in conjunction with a voice alert announcing, "Fire! Fire!". The Kidde Smoke Detector is powered by a 10-year lithium battery, for coverage during a power failure, while eliminating the need for battery changes. When the smoke alarm is at the end of its life span, the detector will announce, "Replace Alarm!". A red LED indicates that the smoke detector is sensing smoke or fire. A green LED light indicates that the smoke detector is operating properly. A test-hush button allows you to test the battery operations as well as silence nuisance alarms that may occur from cooking or shower steam. The Kidde Smoke Detector will chirp when its time to replace the battery, however, an Ambient Light Sensing feature helps to prevent alarm chirping in dark conditions. Install a smoke detector & carbon monoxide detector on every level of your home and near bedrooms to help keep your family safe from fire & poisonous gas. The Kidde smoke detector can be used as a single unit or interconnected with up to 24 Kidde devices (18 of which can be initiating) in a multiple-station arrangement, not exceeding the NFPA (National Fire Protection Association) limit of 18 initiating devices (smoke, heat, CO). It is possible to interconnect 6 strobe lights and or relay modules. UL Certified with a 10-year limited manufacturers warranty. Meets requirements of UL 217, NFPA72 (chapter 11 2002 edition), NFPA101 (One and two-family dwellings), and Federal Housing Authority (FHA).