A closeup view of the equipment of the detector at Harper, Ohio. This is the Servo Hotbox detector with protective ramps built around it to protect it from Dragging Equipment. The Servo has a door that unlocks when a train is on its circuit-the door protects the beam which measures the bearings as they pass over it, and closes when the train is gone. A detector does not know if a bearing is hot, it compares all bearings for any unusual ones. It also keeps a record printed out in the bungalow. Photo by Eric Kretz.