[en] Radiation detectors installed on fixed detection portals are widely used throughout the nuclear industry to prevent radioactive materials from being illegally removed from buildings or sites. These cumbersome and expensive devices detect any abnormal increase in radioactivity levels at various points along routes used by personnel or vehicles. It would therefore seem natural to use the same kind of equipment to prevent illicit trafficking of radioactive materials by installing it at strategic points. We present the parameters which influence the detection of radioactive materials, taking a plutonium-239 source as an example, and show, in our study, how difficult it is to actually detect a radioactive substance. The use of detectors used for real-time dose measurement is another interesting approach for the application. These are small, inexpensive detectors worn permanently by personnel to signal any abnormal dose rates. Although less sensitive than detection portals, they have a wider detection range than any fixed detectors, with a detection closer to the source. (author)