First alert, battery operated combination photoelectric smoke & carbon monoxide alarm, packs premium detection capabilities into a sleek, compact design, comes equipped with a photoelectric sensor & a patented smoke entry system, allowing reliable detection of smoke produced by smoldering fires while keeping false alarms to a minimum, features an advanced electrochemical sensor that detects carbon monoxide leaks from multiple sources such as faulty fuel burning appliances & blocked chimneys, sleekly designed, can be mounted unobtrusively on a wall or ceiling, a loud alarm sounds when smoke or carbon monoxide is detected as well as a voice alert warning of the location & type of danger, note: please check your local building code requirements before installing this product to determine compliance with applicable standards.