Psy-Tracker

Sometimes referred to as aetherscopes, these are a particular form of scanner designed to monitor disturbances in the Empyrean and detect and analyse psychic energies. These sophisticated and tricky devices are used extensively by adepts and savants attached to the Inquisition, although very similar scanners are actually used as a common part of the engineering equipment of major starships to monitor the status of the ship's Geller Field and its generators. Ti takes a great skill to use one of these scanners. The user's awareness is taken in conjuction with the device enable the user to determine the presence and relative strength of psychic force. Daemons, the lingering effects of warp disturbances and the like. Psy-trackers are somewhat temperamental devices with an operating range of no more than a few hundred metres (although they might register very powerful spikes and signals from far beyond that). They are also easily clouded and confused by powerful energy fields and psychic "background noise".

Source

 * Dark Heresy: Core Rulebook (RPG), pg. 191