The Communist police state of East Germany, which had the dubious honour of
having one of the world's most comprehensive spy networks, came up with an
ingenious method of tracking political dissidents:
tagging them with radioactive elements, and following them around with hidden Geiger counters. Former East German dissidents may be relieved to know that the doses used
were usually kept at safe levels, and dangerous mishaps were kept to a minimum.
Ominously enough, East German political prisons contained "unusual non-medical X-ray machines", which may have been used for helping along the cancer-related
mortality rate amongst troublesome dissidents.