The First Alert Combination Smoke and Carbon Monoxide Alarm features a photoelectric sensor that detects the smoke most commonly produced by smoldering fires, providing sensitive detection while minimizing false alarms from cooking or shower steam. The advanced electrochemical CO sensor detects carbon monoxide leaks from multiple sources such as, faulty fuel-burning appliances. Unique alarm sounds and indicator lights on the face of the detector distinguish a smoke warning from a carbon monoxide warning.

（Smoke Test Tunnel ）