The Kidde Wireless Smoke Detector, 10-Year Battery, Voice Alerts, Photoelectric Sensor Wire-Free Smoke Alarm, model p4010ACS-W, is a basic smoke detector that 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, the ring on the detector will turn red, and a voice alert will announce, "Fire! Fire!". The Kidde Wireless Smoke Alarm enables extension of coverage & protection without any need for additional wiring. When one alarm sounds, they all do, providing an early warning against fire by dramatically increasing your ability to hear an alarm anywhere in your home, regardless of where the fire starts. The Kidde Wireless Smoke Detector is powered by a 10-year lithium battery, which eliminates the need for battery replacements, while providing coverage during a power failure. When the smoke alarm is at the end of its life span, the detector will announce, "Replace Alarm!" 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 from chirping in dark conditions. The Kidde smoke detector can be used as a single unit or interconnected with up to 24 Kidde devices (18 of which can be initiated) 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. 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. UL Certified with a 10-year limited manufacturers warranty.