The Merlin Contraband Detector is a portable, lightweight instrument that indicates the presence of hidden material by signalling unexpected changes in the density or thickness of a surface. For example, an "empty" tire filled with air will register a lower reading than one filled with drugs.

In operation the detector emits a beam of energy into the object being inspected and measures the backscatter. As the detector is moved across the surface of the object the measured backscatter is displayed on an LCD digital readout and an alarm sounds if the reading changes.

To operate, the detector is first placed anywhere on the surface of an object and held for two seconds while a "normal" reading is registered. The detector is then moved across the surface of the object and any changes in density will trigger an alarm.

The Merlin 133 Contraband Detector also features a unique radiation detection function which allows the instrument to detect the presence if concealed radioactive material. Audio output resembles a traditional geiger counter in this mode.