While all smoke alarms are designed to detect smoke, different sensing technologies react differently to certain types of fires. The fist alert Sa3210 dual sensor ten year alarm makes use of both ionization and photoelectric sensors to offer the earliest possible warning-regardlesss of the type of fire. Sometimes a fire can smolder for hours before erupting into flames. Photoelectric sensing technology is more sensitive than ionization sensing technology at detecting these sorts of smoldering fires, like those caused by cigarettes burning in couches or bedding. Other fires erupt into flames quickly, like kitchen grease fires or fires fueled by paper burning in a wastebasket. Ionization sensing technology is generally more sensitive than photoelectric sensing technology at detecting these sorts of flaming fires. This alarm is powered by sealed, ten year lithium batteries to provide continuous protection for ten year without battery replacement. Single test/silence button mutes unnecessary alarms and tests function. End of life timer sounds when it's time to replace your alarm. First Alert Sa3210 meets UL217 standards and complies with legislative requirements for 10-year battery operated smoke alarms. This product includes mounting hardware and is backed by a 10 year limited .