How do you handle a non-thief sneaking past a non-thief?
Great question! I usually handle it with a mix of Hear Noise throws and Surprise rolls.
For example, assume a Sneaker wants to sneak across a corridor being watched by a Sentry.
There are three possible cases:
Case 1) The Sentry is alert and actively looking down the corridor, towards the Sneaker. The Sneaker is seen automatically. Most Sentries can’t sustain this level of alertness for very long, though.
Case 2) The Sentry is passively looking down the corridor, but isn’t at a state of high alertness. Roll to see if he is caught off guard - on a surprise roll of 1 or 2 on 1d6, the Sentry is surprised (i.e. off guard), and the Sneaker gets through. If the Sentry is not surprised, you’re in case 1, and the Sneaker is seen.
Case 3) The Sentry isn’t really paying attention to the corridor at all. Roll a Hear Noise check for the Sentry (normally an 18+). If the sentry fails his Hear Noise check, the Sneaker gets through. If the Sentry makes the check, he hears something. But that doesn’t mean he caught the Sneaker in the act. Roll to see if he’s caught off guard (surprised); you’re in case 2.
So, the chance of a non-thief sneaking past an alert sentry is 0. The chance of a non-thief sneaking past a passive sentry is 33%. The chance of a non-thief sneaking past a distracted sentry is 90% (15% chance of being heard x 66% chance of being heard alerting the sentry = 10% chance of getting caught).
If the Sentry had the Alertness proficiency, he’d be surprised only on a 1 in 6, and he’d get +4 to Hear Noise, That would leave the non-thief a mere 16% chance to sneak past a passive sentry (Case 2) and a (1 - (70% x 84% = 58%) 42% chance of getting past a distracted sentry.
This is exactly what I needed. Also, I’m assuming the Thief who sneaks past that same sentry gets his Hide in Shadows / Move Silently check and if fails ALSO gets the same chances as someone who is not a Thief?
Does that make sense? So, the Thief skill acts as a layer on top of the normal method for resolution?
Thanks for super quick response!
Michael, that’s exactly correct. The thief skills are a layer on top.
Great. Many thanks!
Oh, those rules are awesome. bookmarks this page for future reference
That’s a great system (and a nice example of Alertness being an excellent proficiency). Is that in the book? Sneaking around is a pretty common activity.
It’s not in the book, no. It’s sort of an emergent system that develops from the interplay of various different mechanics.
Maybe I should put it in the Additional Rules section in “Secrets”?
Maybe I should put it in the Additional Rules section in “Secrets”?
Longshanks: Yes please.
I agree, it’s a really useful example of how mechanics interact.
Not only is it useful, but (given the amount of interrogation the D&D Thief has been subjected to) it’s a necessary articulation of the relationship between the Thief and other classes. It’s also useful to campaigns that don’t use the Thief at all, and exactly the kind of “best of” ruling on the old system that ACKS promises. Put it in!
Here’s an official rules-style write-up.
SNEAKING
During an adventure, the characters may wish to move through an area undetected. Obviously if there are no guards watching the area, this poses no problem, but if the area is monitored by a sentry of some sort, there is a chance the character(s) will be detected. These situations can be handled through the interplay of the surprise and hearing noises mechanics, with varying risk depending on how alert the sentry is.
If the sentry is actively watching an area, any character(s) attempting to sneak through the area will be detected automatically. While most sentries cannot sustain this level of alertness for more than a turn, constructs and undead are always considered actively alert.
If the sentry is passively watching an area, but isn’t in a state of high alertness, the Judge should make a surprise roll when the character(s) attempt to sneak through. If the sentry is surprised (normally on a roll of 1-2 on 1d6), the character(s) can move for one round without being detected. If the sentry is ready, then the character(s) are detected.
If the sentry is distracted (e.g. by conversation with friends or a loud noise elsewhere) or otherwise not looking, the Judge should make proficiency throw to see if the sentry hears any noise (normally an 18+ on 1d20). If the sentry fails this throw, then the character(s) can move for one round without being detected. If the sentry succeeds on this throw, he hears something which gets his attention. But that doesn’t mean the character(s) automatically got caught. The Judge should now make a surprise roll, as described above.
Under normal circumstances a passive sentry can be circumvented 33% of the time (2 in 6), while a distracted sentry can be circumvented 90% of the time (because he has a 15% chance of hearing something and a 66% chance of detecting the characters if he hears something). If the Sentry has the Alertness proficiency, he will be surprised only on a 1 in 6, and will gain a +4 to Hear Noise. The Alertness proficiency therefore reduces the chance of circumventing a passive sentry to 16%, and of circumventing a distracted sentry to 42%.
If a sentry is watching an area that is dimly lit or otherwise offers some concealment, a thief (or similar class) may attempt to hide in shadows. If the thief is successful, the sentry doesn’t see the thief – he is effectively distracted, as above. The thief will be detected only if the sentry hears him make noise. If the thief successfully moves silently, he cannot be heard. Thus a thief sneaking through a dimly lit area can sneak past virtually any sentry if he successfully moves silently and hides in shadows.
Maybe this should go in Chapter 6: Encounters, as it relates to the party trying not to have one? It also has to do with the possibility that a monster that wins surprise will try to use it to get away undetected - I wrote a little thing about this under Surprise that could be combined.
Also, how do you handle multiple sentries? I had a situation last weekend where a rival party of adventurers was trying to gank the PCs, who were trying to sneak past invisibly. Giving each of the rivals a hear noise check virtually guaranteed one of them would make it because they got so many rolls.
Tavis, its broader than just avoiding an Encounter. If I saw a good place to segue it in I’d so but I haven’t really found one.
As far as multiple sentries, I just generally roll once and then apply the same roll against all the sentries.
How about putting it after Traps and Trap Detection in the Dungeon Adventures section,
and change the first line to something like -
‘Whether they are deep in a dungeon, at large in a city or out in the wilds, the characters may wish to move through an area undetected’
I think the rules write-up could be clearer on “the thief gets the regular checks in addition to their move silently” part.
Also, isn’t hide in shadows only usable while stationary? The way it’s written, it gives the impression that hide in shadows will let you slip by unseen when it seems like noise is the part that counts rather than visibility. I’ve personally always seen hide in shadows either as a “wait for them to pass” sort of ability, or as an “oh shit button” for when you’re about to get noticed. It’s possible I’ve just been looking at it too narrow-mindedly 
Sean - we haven’t introduced the concept of “Surprise” by that point in the rules. That’s not necessarily a deal breaker but still a bit confusing. I don’t have an issue with it just being in Judge’s rules. All of the rolls will be rolls that the Judge makes.
Alex, shouldn’t multiple sentries have a better chance of at least one of them paying attention? It sounds like doing it your way, having many guards isn’t going to be any better than just having one?
Considering how many possible situations there are for sneaking past something, I feel like it’s best left either standardized or up to GM fiat rather than getting down into group size and other details. It’s a very different scenario sneaking across an open area vs sneaking across a guard in a corridor versus just running by an open door vs running from cover to cover, etc. etc.
If you think it’s harder or easier in a given situation, apply the usual +/- to rolls you would in any other situation. Plus, I’d imagine larger groups of guards also have more distractions, i.e. each other, which helps balance things out so it’s not totally unrealistic.
I added a section called “Sneaking and Surprise” immediately after the SURPRISE section of the rules.
This seemed to flow well, since the Surprise concept has just been introduced, the Hear Noise rules were introduced earlier (under Traps), and the Encounters rules have just finished.