Scanners (or multi-scanners, or Auspexes) are Imperial short-ranged devices used to detect motion, invisible gases and energy emissions throughout a wide spectrum, such as heat, radiation and most forms of energy given off by vehicles and living troops. Their main tactical use is to reveal otherwise hidden troops and allow them to be fired on. The standard range of a scanner is fifty metres, although walls more than fifty meters thick as well as certain shielding materials are able to block them.
Scanners can take the form of separate hand-held devices, or they may be built into a helmet such as in the case of Terminator armour. The Imperial Guard uses scanners known as surveyors. Space Marines and other forces use the auspex.[Needs Citation]