At ~ 9:28 PM, Westmoreland 911 dispatched Station 20 (Murrysville VFC) for a Carbon Monoxide (CO) Alarm at a home on Stewart Court. Station 20 responded with Engine 20 (3 firefighters), while Lieutenant 20 responded directly to the scene, and an additional firefighter manning the station. Westmoreland 911 also dispatched Station 610 (Murrysville Medic One) to support Station 20. Lieutenant 20 was first on scene, established command, found that the home's CO Alarm had been activated, and ensured that the home's occupants were safe. Upon arrival of Engine 20 and Medic 611, the firefighters checked for CO using 5-Gas Meters, and the results were negative. Upon investigation it was found that the home's CO Detector was defective, and it was recommended that the home owner purchase a new CO Detector. Command 20 returned all responding units to service and station.