This listing is for a set of TRC-3A seismic intrusion transmitters. These were designed to detect troop movements in the field during Vietnam.
They look to be unused as there is no dirt or grime and the cases and tips are clean as well as the battery compartments. They run on 2 each 9 volt batteries per unit which are not included. This is a complete set of 4 matching units as each has a different progressive number of dots on the unit which I believe signifies the number of beeps transmitted when activated which allows the radio op the means of determining enemy direction. There is no receiver included which would complete the set but you do get the carry bag which also looks to be unused.
From some reading I guess it is common that the clips that hold the probe in place to break. Two of these unit have clips broken and one was apparently tried to be glued on. I would think that they would work unless age can affect this type of electronic. Each has a manufacturers plate that identifies the model number and frequency , as well as the federal stock number and contract number. They are each labeled as being manufactured by Dorset Electronics in Tulsa, Oklahoma.Take a look at the photos as these are the units you will be receiving. The frequency is 147.2 Mhz or identified by the number 2 on each set.
The item "Four USGI TRC-3A Seismic Intrusion Transmitters, 127.4 Mhz, No receiver, VG Cond" is in sale since Friday, November 2, 2018. This item is in the category "Collectibles\Militaria\Surplus\Radios". The seller is "deanbers" and is located in Eagle, Idaho. This item can be shipped to United States.