At ~6.48 AM, Westmoreland 911 dispatched Station 20 (Murrysville VFC) for a Carbon Monoxide (CO) Alarm at an apartment in the Murrysville Apartments. Station 20 responded with Engine 20 (3 firefighters), with 1 firefighter going directly to the scene, and 2 firefighters on station standby. Westmoreland 911 also dispatched Station 610 (Murrysville Medic One) to support Station 20. The direct responding firefighter and Medic 615 were first on scene, with the direct responding firefighter establishing the command, and the apartment occupant out of the building. Engine 20 arrived, its crew entered the building using 4-Gas Meters to survey the apartment for CO. No evidence of CO was found, and after further investigation it was found that a defective CO Detector had caused the alarm. Command 20 returned Engine 20 to service and station.