First Alert, 2 pack, 10-year battery operated slim design smoke alarm provides the same protection as a standard smoke alarm while taking up only a fraction of the space. The alarms feature a built-in lithium-ion battery that provides continuous power for up to a decade. Equipped with an ultra-reliable photoelectric sensor, the smoke alarms detect smoke from slow-burning, smoldering fires while keeping false alarms to a minimum. A patented smoke entry further enhances the detector's reliability by providing a direct path to the smoke sensor. The simple twist-lock mounting system installs easily onto a wall or ceiling, while the tamper-resistant locks help prevent removal of the battery to keep the alarms secure. A loud 85 dB alarm sounds when smoke is detected and a convenient test/silence button lets you easily check alarm function and mute false alarms.