Combination smoke and carbon monoxide alarm – Smoke and CO sensing technologies work together to detect real fires faster and reduce cooking-related nuisance alarms. Sealed-in lithium battery – Sealed-in lithium power supply; No battery replacement required over the 10 year life of the alarm. Eliminates worry about battery removal or unauthorized deactivation of alarm. Photoelectric Sensor – Smoke alarm contains advanced photoelectric sensor that may detect visible particles (associated with smoldering fires) sooner than ionization alarms. Self-activation – Alarm automatically activates when attached to the mounting bracket. Alarm memory – Rapidly flashing LED alerts user if the alarm has sounded since the last time the test/reset button was used.