Ok, so I have a techmarine in my group who has an augur array implant, and it's making things kind of difficult for me. I'm putting the rules text in here for reference:

" These devices are used to detect energy emissions, motion, and biological life signs. A character using an auspex gains a +20 bonus to Awareness Tests and may make a Tech-Use Test to spot things not normally detectable to human senses alone, such as invisible gases, nearby bio-signs, or ambient radiation . The standard range for an auspex is 50m, though walls more than 50cm thick and certain shielding materials can block the scanner. "

So here's my issue: I would like to use environmental hazards, surprises, etc. in my missions (e.g. I think genestealers are fun), but my techmarine is constantly asking to "scan for life signs" or "scan for motion" whenever they are about to move into a new area. Being a Techmarine, passing the Tech-Use test is pretty much guaranteed for him, and I feel a bit frustrated with how that seems to rule out a huge number of options for me.

On the other hand, I don't want to be constantly making up excuses for why the auspex won't work (one player even made a joke about this, asking "is this one of those situations where it doesn't work because... reasons?")

So my questions are: how do auspexes get used in your games, typically? What do you consider acceptable parameters for what they can/can't do? Any suggestions for how I can handle this without making my player feel like I'm singling him out/hitting him with the nerf bat?

It costs a standard action to scan , no? so if he constantly delays have him stay behind the rest of the team. In my games i had rulled that the Warp could affect auspex. Also if they are moving in such close formation so as to have a 50 m "bubble" around them maybe add the hazard "Unstable (see collapsiible) Footing. Also remember that corners by definition stop scans and there are things out there that can charge 50m.

You can have an 'orgy' of evidence as they say in Minority Report. Consider this scenario. Marines are in the jungle. They are being hunted by a Lictor. Sure they can spot it's movements withheld auspex but how do you distinguish that from all the other movement lifeforms etc. Then it's not simply a tech use tech test to operate the auspex but a scholastic lore beasts and forbidden lore xenos test. But ultimately marines generally won't be caught out by your average ambush

Yeah, that's a tricky problem. One thing to keep in mind is that an auspex is absolutely not a Star Trek -style tricorder- it doesn't scan a broad range of data and compile an overall picture. An auspex is much more limited: it only scans for the one specific thing that the operator tells it to look for. So, if you are specifically scanning for 'nearby bio-signs', you will not pick up on the non-living mechanical trap you are approaching. If the auspex operator insists in cycling through every possible scan mode at regular intervals, make the delay that would involve become its own punishment.

You can also rule that interpretation of readings may require rolls on a Lore Skill. Using Visitor Q's example above, if the Techmarine wants to distinguish between the bio-signs of the Lictor they are hunting and a common tree sloth, he needs to make a Lore: Scholastic (Beasts) roll. Deos he have that Skill? Didn't think so...

Also, the genestealers you want to use are probably smart enough to hide behind '50cm thick' cover.

Scanning technology in many sci-fi universes can be disrupted or interfered with by a number of factors. Intense electromagnetic activity, radiation or temperature extremes are all things which have been known to mess with equipment to the point that they are not working properly. What's worse is that nothing says the device is even working at all, we have probably all experienced times where we think a device is functioning normally (usually a mobile phone charger) and we rely flawlessly on its output and use and yet only when put under intense scrutiny do we realise that it is in fact, defunct. You could use this as a GM to your advantage and rather than say they cannot use it or it is broken, give them a false positive. The wording as written says it detects biological life signs. It does not state how big the life sign is that it is detecting and just says "yep I can see a bio signature here". So essentially they could get blips around them, think they are being stalked by genestealers, open fire on all the walls only to realise there are tons of rats nearby. False positives makes them complacent and leaves them vulnerable. You are giving them readings but without a master crafted auspex you wont be giving them the size of the creature, the exact strength of the radiation, how fast its moving etc.

The alternative is that it is possible for the xenos such as the Tyranid (or other alien races) depending on where they are and what the setting is, to have adapted to counter visual and/or electronic detection more effectively and have been bred to counter this. Look at a stealth bomber which effectively reduces radar detection by having a surface which absorbs the radio waves as well as having a shape which reflects and distorts the true picture. An auspex will likely work the same by emitting signals and reading the bounce backs. You could indeed have such Tyranid species develop to resist this quite easily, bred by the hive mind to avoid detection by electronic measures and the eye.

So, a few things:

1) The Auspex, as noted, is limited in what it does. It calls out the three things it can detect, and though movement, energy, and life signs are very useful and broad categories, as indicated, it does absolutely nothing for other things- such as detecting hiding places, hollows in walls, etc. Just because they detect life signs does *not* in any way give them an automatic detection of the creature involved. It is *entirely* fair to say "you detect 3 life signs ahead", and then laugh an evil laugh as the group freaks out and debates over how to advance because they don't see anything, then as they cautiously advance have some rats (or equivalent) scurry out, causing them to breathe a sigh of relief, before the lictor drops down from above right on top of them. Play mind games with them, sometimes the presence of some information can be far more dramatic, suspenseful and terrifying than complete ignorance. The adage holds true: Space Marines may know no fear, but players sure do.

(as a note with this, I would definitely *not* allow (regardless of any checks) the TechMarine to differentiate different types of life signs. Blips on the radar is all I would give them, and I see nothing in the rules that indicates they have any way of getting more detailed information regarding what those blips represent.)

2) Auspex is limited in range. 50m is a run action followed by a charge action for many of the faster creatures out there. If he's actively using his auspex, getting 6 seconds of warning is fair, and hardly going to allow much more than an identification of exactly how much trouble they're in. If he's not actively checking it every 6 seconds, it's not just reasonable but likely that he didn't scan at exactly the right time to see the life signs or movement swarming in from around the corners or tunnels around them. Just because that 50m room they are walking into was scanned before they stepped in and was clean then, doesn't at all mean it will stay that way. By the way, if you have nice secure doors distinctly separating every room, stop it. The caves dug in through the walls, or the doors ripped off their hinges, or the windows blown apart can all provide warnings and hints, and increase dramatic tension, and again if you vary what actually happens when they encounter such things you can return the element of surprise to the game.

3) The tech use test does *not* replace awareness tests. They get their +20 to awareness, sure, but something stealthed and concealed has its concealment opposed by awareness, not tech use. The tech use is required if they are attempting to detect something not normally able to be detected with human senses alone, and depending on how you interpret it, they would need to pass both the tech use test *and* the awareness test to pick it up at all. Even if you allow for the most generous interpretation, that they get the "not normally detectable" information with the tech use, that's *all* they get. Neat, you're scanning for movement. In a jungle. You detect it, all around you. Again, I would not under any circumstances allow any tests to discern additional information, in terms of what is causing that motion, or what comprises those life signs. If you want to spot those things lurking in the shadows, you must *actually* spot them, not just stare at your radar screen.

Edit: I really like Calgor Grimm's note regarding Tyranids and evolved countermeasures. If they're fighting parts of the same hive cluster, it not only makes sense from a fluff and in game standpoint, but can help to add emphasis regarding both the permanence and evolving nature of the game world around them for the tyranids to realize they are being tracked down by auspex scanners all the time and evolve countermeasures to partially or fully defeat them.

Btw you can use this all to your advantage as a story teller to have the creatures whatever they are becoming smarter. Early on the bad guys might get blasted easily but then they start to learn.

Low tech solutions to high tech problems:

Auspex can't scan if a walkway (is sabotaged so it) can't hold a marine's weight.

Send the team to a spacehulk, hive, manufactorium and drop 'em down an elevator shaft/ smokestack/ crevasse, preferably into a nest of genestealers/ reactor furnace/ adamantium spikes/ web of tripwires hooked to melta bombs and demo charge.

It's up to you to determine if the auspex can detect explosive devices. If not, simple booby traps (tripwire+ meltabomb) will work.

Things that will interfere with the auspex:

Walls several meters thick, as in say, renegade hives, some space hulks, etc.

Background radiation might be constantly setting it off, play havoc with it.

Chaos. Daemons don't show up on auspex (very very veeeery maybe if you are a grey knight techmarine)

Have innocent bystanders running around.

Back when GW first released Necrons they could jam technology, maybe you can have the tomb lord shutting down their advanced scanners a stuff.

Just because they can see it moving doesn't mean you can't use it to lure the players into a trap.

Auspex? Who uses one of them?

My group goes meh and runs ins guns blazing.

Auspex? Who uses one of them?

My group goes meh and runs ins guns blazing.

Yours even runs in? Mine would have blown it up from a sector away probably by trying to crash a ship into it and setting off its plasma reactors.

As mentioned being beyond 50 meters is a great way to neutralize it. In the spacehulk video games they often had the hive mind blind the sensors.

Put them in a fast moving situation where they have to keep using full moves to stay ahead and then he can't spend the action to read- and even if he does, he'll out range his readings next run move.

These are some excellent suggestions. Thanks, everyone!

Blips on the radar is all I would give them, and I see nothing in the rules that indicates they have any way of getting more detailed information regarding what those blips represent.)

This brings to mind the motion sensors from Aliens. Gives you the range of the target but not what it is.

These are some excellent suggestions. Thanks, everyone!

So, how did it go? Assuming you have played yet....

Haven't had another session yet (next weekend, probably), but I'll be sure to let you guys know how things play out. I think it's going to be pretty memorable