At ~ 3:12 PM, Westmoreland 911 dispatched Station 20 (Murrysville VFC) for a Carbon Monoxide (CO) Alarm at a home on Forbes Trail Drive. Station 20 responded with Engine 20 (4 firefighters), with Assistant Chief 20 going directly to the scene. Westmoreland 911 also dispatched Station 610 (Murrysville Medic One) to support Station 20. Assistant Chief 20 was first on scene, established command, and ensured that the occupants of the home were out of the structure. Upon arrival of Engine 20, Medic 616 and Support 610, Engine 20's crew entered the home with 4-Gas Meters, while the Station 610 EMS personnel assessed the home's occupants. The firefighters found no levels of CO, and upon investigation found that the home's CO Alarm was defective. Command 20 recommended that the homeowner purchase a new CO Detector for the home. Command 20 released Engine 20 for return to service and station.