At ~ 6:58 AM, Westmoreland 911 dispatched Station 20 (Murrysville VFC) for a Carbon Monoxide (CO) Alarm at a home on Forest Ridge Court. Station 20 responded with Rescue 20 (3 firefighters), with Chief 20 and Assistant Chief 20 going directly to the scene. Westmoreland 911 also dispatched Station 78 (Sardis VFC) and Station 610 (Murrysville Medic One). Assistant Chief 20 was first on scene, and established the command. Chief 20, Engine 78, Medic 616, and Rescue 20 arrived. Chief 20 assumed the command, and the interior firefighters entered the structure and surveyed the home using 4-Gas Meters. It was found that a defective CO Detector had caused the alarm. Command 20 recommended that the home owner replace the CO Alarm, and returned all responding units including Rescue 20 to service and station.