The First Alert(R) battery operated smoke alarm with battery backup comes equipped with an ultra-reliable ionization sensor to provide the earliest possible warning of a fast-flaming fire. The sensor is optimized to detect flaming fires, such as those caused by paper, kitchen grease, and other fast-combusting materials. A mute button has been included to serve the dual purpose of silencing nuisance alarms brought on by cooking smoke and shower steam. The combination of a 9V battery and an increased emphasis on the unit's 85 dB sound output gives peace of mind. An end-of-life signal will notify you when the battery will have to be replaced. This product is backed by a 10-year limited warranty.