Marknorth sent this information a while back, about making a device as described in his story The Device. (To read the story, it’s in three parts in Marknorth’s author page in the Prison Library …. click here and scroll down.
Here’s what Marknorth says,
Attached is an overview of existing technology that could be easily adapted to create a version of “the device” from my story.
Although not “self-contained” as the one in the story, it would be relatively easy for the chastity slave to carry the transmitter. The range for control is also limited to 7 miles (maximum with no interference), but the GPS tracking ability is wide-ranging.
Obviously, the equipment is for tracking and training dogs, but the idea carries over. The cock-ring modification is one of the smaller rings from my CB6K.
And here is Marknorth’s diagram (click to enlarge):