In East Berlin, a Stasi officer shoots a radioactive bullet at a diplomat's car tire with an air gun. An informant uses his handkerchief to dust two chairs in a hotel room in Zurich with a chemical substance that fluoresces under ultraviolet light. Another informant applies a liquid substance that sniffer dogs can identify to a suspect's clothes. An intelligence officer applies a radioactive substance to a West German five-mark bill. And an informant brushes a dissident's manuscript with the radioactive isotope barium, which emits gamma rays picked up by a vibrating radiation detection device.

All these scenarios illustrate the use of a chemical or radioactive substance to track objects or people. Such techniques have been used by the world's most powerful spy agencies, like the Soviet Committee for State Security (KGB) and the CIA. Secrecy still surrounds methods used by existing intelligence organizations, but the files of the former East German Ministry for State Security offer us the first detailed glimpse into how “spy dust” was used for surveillance and intelligence purposes.

Since the end of the Cold War, even more sophisticated technological devices have been developed to track new enemies of the state, such as terrorists. We seldom think about the possible dangers or weaknesses of these methods, even though history documents a long list of abuses in the name of state security. The Cold War spy dust story can offer us insight into the limits and possibilities of technology in security even as it is practiced today.