DESC: First Alert Combination Smoke and Carbon Monoxide Alarm utilizes electrochemical carbon monoxide sensor for increased accuracy. You want to be immediately notified where the danger is in your home, to make the best decisions possible in an emergency situation. The alarm features an easy access battery drawer, no need to remove alarm from ceiling to change battery and comes with 5-year limited warranty. Smoke and carbon monoxide alarm meets UL standards. Smoke alarms should be placed in every bedroom, and at least one on every level of the home. The carbon monoxide alarm should be placed on every level of the home and one in each sleeping area.