At ~ 1:31 AM, Westmoreland 911 dispatched Station 20 (Murrysville VFC) for an Automatic Fire alarm (AFA) at Walnut Hollow Plaza #2 on Willian Penn Highway. Station 20 responded with Truck 20 (2 firefighters including Captain 20), with an additional firefighter on standby at the station. Westmoreland 911 also dispatched the following stations to support Station 20: Station 22 (Export VFC), Station 64 (White Valley VFC), Station 78 (Sardis VFC), Station 87 (Harrison City VFC), and the Murrysville Police. Truck 20 and Engine 22-1 arrived on scene, Captain 20 established command, and observed no fire or smoke coming from the structure. Upon investigation it was found that one of the stores was under renovation, and the rehab crew had broken a sprinkler head which activated the AFA System. Command 20 cancelled all enroute units, the sprinkler water supply was turned off, and using the "Knox Box" Entry keys, the firefighters entered the adjoining store to find water damage from the broken sprinkler head. Command 20 notified Westmoreland 911 of the water damage in the adjoining store, and requested that the keyholder be notified of the damage. Once the adjoining store was secured, Command 20 released Truck 20 and Engine 22-1 for return to service and station.