At ~9:05 AM, Westmoreland 911 dispatched Station 20 (Murrysville VFC) for a Carbon Monoxide (CO) Alarm at a home on Trefoil Drive. Station 20 responded with Engine 20 (3 firefighters), with Assistant Chief 20 going directly to the scene, and 3 firefighters on station standby. Westmoreland 911 also dispatched Station 610 (Murrysville Medic One) to support Station 20. Assistant Chief 20 arrived on scene, and established the command. Engine 20 arrived, and its crew used 4-Gas Meters to survey the interior of the home, and found no evidence of Carbon Monoxide. Upon further investigation it was determined that a bad CO Detector had activated the alarm. Command 20 returned Engine 20 to service and station.