The Battery Powered Smoke & Carbon Monoxide Alarm (2-AA batteries included), is equipped with self-testing components that are always checking to make sure the alarm is on & working. This smoke & CO combo alarm helps protect you & your family from 2 dangerous threats – fire & carbon monoxide – in one unit. What's more, the included mounting bracket makes installation quick & easy. Battery-powered smoke alarms provide reliable detection even during power outages, for extra peace of mind.Leading authorities recommend that both ionization & photoelectric smoke alarms be installed to help ensure optimal detection of the various types of fires that can occur within the home. Ionization sensing alarms may detect invisible fire particles (associated with fast flaming fires) sooner than photoelectric alarms. Photoelectric sensing alarms may detect visible fire particles (associated with slow smoldering fires) sooner than ionization alarms.Alarm Warnings – featuring multi-color LEDs Fire: The red LED will flash in sync with the alarm pattern (3 long beeps). The alarm will repeat this pattern until the unit is reset or smoke is eliminated.Carbon Monoxide: The red LED will flash in sync with the alarm pattern (4 quick beeps). This continues until the smoke & carbon monoxide alarm is reset or the CO is eliminated. Low Battery: One chirp & amber LED flash per minute.Alarm Memory: Alerts a user if smoke or CO has been detected in the last 24 hours. If smoke has been detected, the red LED blinks every 15 sec. If CO has been detected, the red LED blinks twice every 15 sec.