Kidde Fire Sentry Smoke Detector, 9V Battery Powered Smoke Alarm, 4 Inch Compact At only 4-inches in diameter, this is one of the smallest smoke detectors you can install in your home, RV, and mobile home Basic ionization smoke alarm, affordable and simple to use to provide detection of dangerous smoke or fire Operating on a 9-volt alkaline battery, the Kidde smoke alarm provides reliable detection of smoke or fire, even during power outages Easy installation ? this basic smoke detector requires no wiring An 85-decibel alarm sounds a red LED indicates the smoke detector is sensing smoke or fire Test-Hush button makes it easy to test the smoke detector and silence false alarms that occur from cooking or shower steam UL listed with a 3-year limited manufacturer warranty on alarm only (not a battery performance claim). It should be assumed that replacement is needed.