The first alert sco5cn combination smoke & carbon monoxide alarm detects both smoke & carbon monoxide in a single device with its dual permanent sensors. This carbon monoxide & 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 & 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, & generators running inside or too close to homes. Requiring just two aa batteries & featuring an easy-access battery compartment for quick changes, this smoke & carbon monoxide detector has unique alarm sounds & 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.