First Alert SA305CN Smoke Alarm with Long Life Lithium Battery Help keep your family safe with this battery-powered smoke alarm; the extended-life lithium battery effectively provides up to 10 years of monitoring Alarm features an ionization sensor for smoke detection, which is effective in recognizing smoke from flaming fires such as paper and grease fires Battery-operated unit provides continuous monitoring even if there's a power failure; plus, it's easy to install Alarm also features loud 85-decibel alarm, a single test/silence button, and EZ-Access battery door To ensure complete protection make sure to place one on each level of your home and in each bedroom