Defect Detectors Rev. 3/20/16

A defect detector is a device used on railroads to detect axle and signal 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. Defect detectors were one invention which enabled American railroads to eliminate the caboose at the rear of the train, as well as various station agents stationed along the route to detect unsafe conditions. The use of defect detectors has since spread to other overseas railroads.

Defect Detector with Audio

The photos are of the defect detector on the FEC mainline in S. Lucie County, Fl. at Walton Road, north of Jensen beach.

The audio was recorded online listening to the Broadcastify Folkston, Ga. area feed. The detector is on the dual CSX mainline mile A610.6 between Boulogne and Callahan, Fl. Listen to the end.

More information at the Trains Magazine website. Always a good source.
Several other videos on YouTube. 

EDIT March 20, 2016 to add  some still photos

Hotbox or Hot Bearing Detector

Dragging Equipment Detector

Laser Detector

Lasers shine down on each side of the passing train. Anything that cuts through the beam will be counted as a defect.

Control box and VHF Antenna

Overview of hotbox and dragging equipment detectors with one leg of bridge that holds laser detectors.