One of the tactics employed by submarine commanders for evading detection by craft equipped with listening devices was to set the sub down under water and turn off the engines, effectively rendering the submarine silent and undetectable.
An early ASW device designed to detect submarines hiding in this fashion was the trailing wire, a long reel of phosphor-bronze wire with a metal weight on the end, connected to a device that sounded an alarm when the weight or the wire struck a metal object.
These excellent photos of the trailing wire device show the indicator installed in the pilot house, and shots presumably taken in a testing laboratory showing the complete device.
Photos courtesy of the Harvey Hayes Family Archives. Thanks to Roy Manstan for the scans, and for arranging permission to post them in The Subchaser Archives.
Roy notes that in the photo showing the alarm unit in the pilot house, the manufacturer's plate indicates Western Electric as the maufacturer.