The First Alert SCO5CN Combination Smoke and Carbon Monoxide Alarm features dual sensors to detect both smoke and carbon monoxide in a single device. A photoelectric sensor detects the smoke most often produced by smoldering fires, and minimizes false alarms from cooking smoke or shower steam. Additionally, the advanced electrochemical CO sensor detects carbon monoxide leaks from multiple sources, such as faulty fuel-burning appliances, blocked chimneys, and generators running inside or too close to homes. A loud, 85-decibel siren alerts you to the threat; unique alarm sounds and indicator lights on its face distinguish a smoke warning from a carbon monoxide warning. This carbon monoxide and smoke detector is battery operated, so you don't need an electrician for installation. Requiring just two AA batteries and featuring an easy-access battery compartment for quick changes, this smoke and carbon monoxide detector has a single button that allows you to silence a false alarm or test the unit.