Defect detector

A defect detector is a wayside device used on railroads to detect problems in passing trains. The detectors are normally integrated into the tracks and often include sensors to detect several different kinds of problems that could occur, including overheating axle bearings ("hot boxes") and dragging equipment. When rolling stock passes by a detector, an automated readout notifies the crew of any defects via radio. Defect detectors were one of the inventions which enabled American railroads to eliminate the caboose at the rear of the train, as well as various station agents placed along active routes to detect unsafe conditions. The use of defect detectors has since spread overseas to other railroad systems.