Genuine U.S. Vietnam War era TRC-3A detector & GSQ-151 instructions. This geophone type detector would be connected to a radio receiver, when set-off by an intruder the detector would send a signal to the radio receiver to let the operator know exactly what era has been breached. Was made by Dorset Electronics USA and is dated 1970. Comes with facsimile instructions for the GSQ-151 anti-intrusion set that uses the TRC-3A detectors, the instructions are dated 9th December 1969.