The Kidde Fire Sentry Smoke Detector, 9V Battery Powered Smoke Alarm, 4 Inch Compact Design, model i9040, is a smaller designed, 4-inch diameter smoke detector that you can install in tight spaces in your home, your RV, or mobile home. The Kidde Smoke Detector uses ionization sensor technology to detect invisible fire particles (associated with flaming fires) sooner than photoelectric alarms. When smoke or fire is detected, an 85-decibel alarm will sound. The Kidde Smoke Detector is powered by a 9-volt battery, which provides easy installation since the alarm requires no wiring, plus coverage during a power failure. A red LED indicates that the smoke detector is sensing smoke or fire. 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 it's time to replace the battery. 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 3-year limited manufacturer's warranty. Meets requirements of UL 217, NFPA72 (chapter 11 2002 edition), NFPA101 (One and two-family dwellings), and Federal Housing Authority (FHA).