Is there any reason for Stealth Suits to turn off "Active Mode". It does seem to be an unbelievably good combat ability, and there does appear to be no penalty at all for them not to use "Active Mode".

comradeda said:

Active mode can alert enemies to the presence of the Stealth Suit Team (there's a separate chance of detecting the interference produced by a Stealth Suit on Active)... Passive Mode doesn't have that risk, making it better for an undetected approach against unaware enemies, particularly when conditions are in the Stealth Suits' favour (such as at night, where Awareness Tests are typically more difficult).

But they only have -10 for passive mode. In active mode, they get -30 to even detect the "fuzzy screen", let alone actually being able to see them, which there appears to be no rules for whatsoever.

Stealth suits can be a little hard to figure out at first, just bear the following in mind.

Concealment is always an opposed test, you only make such a test when someone looks at a character attempting to conceal himself. Silent move is opposed as well.

Now, stealth suit operators do have the odds stacked in their favour. The pilot has agi 38 and concealment +20, so right off the bat he tests on a 58. His stealth armour gives him -10 to any awareness tests to see him in passive and -30 in active. The pilot does not have any bonuses to his silent move so that test would be on straight 38. There is also the rule, any armor that provides 7+ ap gives the character a -30 to concealment/silent move tests, although I'd think a specialist suit like this would counter the rule but I have found nothing specifically stating the stealth suit ignores this rule.

On the other hand there are a few things that will make you immediately detectable. One being attacking, once you make an attack you immediately reveal your presence. This is backed up in Dark Heresy: The Inquisitor's Handbook in the expanded skills section on page 228. Either the noise, muzzle flash, or the rounds in the air are giving you away. The Inquisitor's Handbook states you can take a half action to hide yourself again (with the target getting a +20 to awareness test) but if the suit fired its burst cannon then it can't that turn (burst cannon only fires full auto which is a full action). Next turn it may attempt to hide again with concealment, remembering concealing one's self is a half action in itself. And no, the stealth suit doesn't have a silenced burst cannon. Other things that may give a stealthed character away, jumping/running in water, flying dust, or running (literally) into an enemy. But these are all in the purvue of the GM.

Assuming the stealth suit ignores the -30 penalty for ap. When a stealth suit tries to sneak its pilot tests at 58 with a bonus of +10 if the pilot stands still (as per the concealment skill). So the Tau pilot would need to roll under 58 or 68 if remaining still when in either mode simply to succeed in concealing himself. If he fails the roll then he can be seen or heard by anyone. Since the concealment roll is opposed, you must keep track of his Degrees of Success (DoS). A roll of 49 would be a pass, but with 0 DoS, 48 equals 1 DoS. Now if he were to have made himself detectable and stealthed in the next turn the GM may want to give the players some modifiers, not too much, for a turn or two (if the suit stays near its last known location) to represent the players being aware the Suit is out there and of its general location (as long as the players are looking for it of course).

A Tau stealthsuit pilot is more likely to give himself away via sound more often than sight. A stealth suit pilot only tests on 38 for SIlent Move, and in passive mode the opposing character has no penalty to detect him. Active mode still gives -30 to awareness tests against the pilot's silent move. Although with a skill test of 38 there is a greater chance the pilot will fail the test and be heard (stepping on a twig or scuffed his feet) compared to his concealment test for sight based detection, even on active mode. Of course the suit must be pretty close to the characters to be heard if it is sneaking, less than 15-25 meters depending on the environment.

Assuming a normal human (Per 30) were lookeingin the direction of a stealth suit. If it were in passive, the man would need to roll under 20 to see the suit, but only under 30 to hear it (passive mode only effects visual senses). But he would technically be unable to detect it if on passive as he'd need to roll under 0 to detect him (assuing your group doesn't use a 01 = always succeed), even with hearing I believe. So if the Tau pilot rolled a 49 (0 DoS) and the Human rolled a 10 the human would detect the suit if its in passive mode (with 1 DoS), but not if it were in active (failed roll).

Space Marines have enhanced senses, with +10 to sight/sound without helmet and +20 with. A space marine (Per 45) would test to detect the stealth suit above on a 55 if on passive or 35 on active. The same roll by the Tau as above (49) would mean a space marine would not detect a suit in active mode if he rolled 26 or higher (26-35 = 0 DoS so the Tau suit would win the tie 36+ is a failed test). But if the marine rolled 25 or less he would have detected the suit (25 is 1 DoS, the suit pilot with conceal roll of 49 had 0 DoS).

FInally, If a person use a device the suit is jamming to detect the suit, such as an auspex or auto senses, as long as the user passes his awareness test by 1 DoS he notices something is jamming his equipment. Example: A Tau Stealth suit in active mode rolls a 07 to conceal himself getting 5 DoS. A space Marine rolls a 23 for his awareness test giving him 1 DoS. The space marine did not detect the stealth suit because the Tau pilot won the opposed skill test with a 5 to 1, but the space marine can tell something is out there messing with his helmet auto senses because he got 1 DoS on his awareness roll.

Hopefully that helped a bit. Sorry for the long exposition, but the stealth suits are fairly difficult to understand, primarily because concealment isn't as well described in the rulebook as it probably shoudl be.