The Kidde Plug-In Carbon Monoxide Alarm with Battery Backup plugs directly into your standard wall outlet making installation quick and easy. The backup is powered by 9 volt battery and will work during power outages. It has two LED indicators, a test button, low battery hush, and a tamper resist feature that alerts you if the unit is unplugged. No wiring required for installation. 5 inches wide by 3.8 inches tall.