The First Alert SCO5CN Combination Smoke and Carbon Monoxide Alarm detects both smoke and carbon monoxide in a single device with its dual permanent sensors. This carbon monoxide and smoke detector is battery operated, allowing you to easily install it without requiring an electrician. A photoelectric sensor detects the smoke most commonly produced by smoldering fires and minimizes false alarms from cooking smoke or shower steam. 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. Requiring just two AA batteries and featuring an easy-access battery compartment for quick changes, this smoke and carbon monoxide detector has unique alarm sounds and indicator lights on its face that distinguish a smoke warning from a carbon monoxide warning. A single button allows you to silence a false alarm or test the unit.