A player in my game has asked if there is a way to suppress or hide the fact he is a psyker. A cursory glance through the books reveals a number of options to empower or alter how their power works, but not much else. Am I missing something or are psykers pretty much walking beacons of power to those who can sense it?
@aramis has a point in his answer. But psykers can cloak their presence, I'm sorry I don't have my book here with me, but I had the impression that there was a psychic power for doing this -as strange as this might seem (also, i might have seen this power in Black Crusade). If that's not the case you can always decide that a Psyniscience test can be used to try and cloak your presence - then you would make opposed checks with whoever was trying to detect the psyker.
In the Dark Heresy book they present us a pre-made sector as you all know well. The Lord Inquisitor of this sector is secretly a psyker, a fact unknown to the other members of the Inquisiton. If a psyker could always detect another, there was no way for his "talents" to remain unknown to his fellow inquisitors - and probably he isn't a sactioned psyker either, cause if he was the other inquisitors would obviously know it (at least most of them).
This ability might make for a nice, if unusual elite advance.
Talent: Unremarkable warp signature
Pre-requisite: Psy-rating & Deceive talents
Description: If the psyker has no psychic power active, they appear to psynicience to be a mundane individual with average human psi potential. At the cost of a temporary fate point, the psyker can extend this effect for the remainder of the session even if he or she has powers active.
Beware though, if PCs can have this, then so can NPCs. Never again will you be able to trust your psyker to be able to tell if one of those pesky cultists is actually a filthy sorcerer. *8')
Incidentally, in one Dark Heresy game that I've played in, all characters except the psyker rolled themselves a psy-potential rating from 0 to 99 (the psyker automatically started with 100).
Events in game allowed the psy-potential to go down (my tech-priest embracing the machine or our guardswoman gaining a True Faith Talent) and up (the psyker gaining a higher psy-rating, or our radical assassin discovering he was a nascent psyker). We were even given special dispensation by our Inquisitor to use the xenos 'e-meter' we found, which my tech-priest calibrated so he had a shot at spotting sorcerers even when the psyker was otherwise disposed (usually yet another peril of the warp *8).
Overall it added a lot to our game.
Psykers are not automatically all-the-time obviously psykers. (If this was the case, it would be rather harder for psyker inquisitors to go about unnoticed.) So the real question, rather, is what gives you away as a psyker? Here's what I've come up with:
- Obvious sanctioning side-effects
- Use of obvious psychic powers (bio-lightning, just about any pyromancy power, etc.)
- Invoking psychic phenomena and/or perils of the warp
Note that, depending on the specific powers and phenomena being used, it may be obvious that somebody around here is a psyker, but it may not be obvious who the psyker is. Other times, the psyker is the visible epicenter or origin. However, even if the source is not obvious, NPCs may be able to figure out who the psyker is. (Hint: it's the guy in the robes with the staff who keeps muttering to himself.)
Finally, anybody with access to the Psyniscience skill can automatically test it (like Awareness) to notice warp disturbances (like the usage of psychic powers) and, with enough successes, determine the origin (i.e. the psyker.) However, psyniscience is normally only available to psykers, so it's sort of a "I can sense you, Highlander!" thing.
Finally, note that daemonic entities are always detectable with Psyniscience, and although Untouchables are (by definition) not detectable by Psyniscience, they do make even non-psychic people uncomfortable.
tl;dr You can't detect a psyker unless they use psychic powers, and even then there's no guarantee unless you're also a psyker.