Multiple Spot/Listen checks with one roll?

[Quasqueton]

What's a good way to make several Spot/Listen checks with one die roll?

Say a rogue is trying to sneak past a dozen guards. How can I make Spot/Listen checks for them without rolling two dozen times? Is there a rules-based concept to go with on this?

I've thought about rolling for one guard and then adding +1 for every additional guard who would be making a check. But then you could get a situaion where a bunch of guards with only +2 to their checks get a 28 result.

Quasqueton

 

[usdmw]

Well, it's probably more trouble than it's worth, but you could just use the multiplicative property of probabilities. For example, if a character has a 50% of success on a Spot check (Spot +5, DC 15) and he needed to make 5 spot checks, his chance of succeeding on ALL of them would be:

50% ^ 5, or .5 * .5 * .5 * .5 * .5

The math is pretty easy, but I'd just roll a few times.

 

[Scion]

Bunch of guards, close together. I dont think assuming that they are all effectively 'aiding' one another, within certain restrictions of course.

So, one roll with a +2 for each is not completely unreasonable. Although personally I would probably make them groups of 3 or 4 and cut the rolls down that way while each roll gets a nice little boost.

 

[nimisgod]

Also, you can just assume that all the guards took 10 on their listen/spot rolls

 

[Whimsical]

I think that the math answer is good if you are willing to do it. I think that the Take 10 answer is not a good idea since the guards are not benefiting from having each them getting a check which is one of the value of having multiple guards in one area.

I think an efficient method is, if all of the guards have the same score, to determine what is needed on the die roll to spot the hidden dude, then roll multiple d20s simutaneously. So, if you know that a guard needs to roll a 16 on the die to hear the rogue (guard has Spot of 2, rogue rolled an 18 on his hide check), then roll 4d20 and just quickly scan for the number or better on the dice. Roll again for the next set, etc.

 

[AuraSeer]

If they're just regular city guards, who are on ordinary watch duty like they are every day, I always assume they're taking 10. If they've just been put on alert, or they know an attack is on the way any minute, I roll for each of them.

When two guards are watching the same area, and they can talk to each other, I give them the +2 bonus for Aid Another. Also, each time the number of watchers doubles, I add an additional +2. (For twelve guards, the total bonus would be +6.)

I haven't worked out any of the math behind this, but it seems to work all right in practice. A good rogue can sneak past one or two guards fairly easily; a small group is harder, but doable. A large group of guards is tough to get by, but a high-level rogue can still pass a whole army of low-level watchers with little chance of detection.

 

[dcollins]

What's a good way to make several Spot/Listen checks with one die roll?

Yes, I use the PHB "Cooperation" skill rules for this situation. Estimate a percentage of helpers who would make the DC 10 Cooperation check, and add +2 for each of those. Compare to the hiders, who I usually assume all Take 10 on their hiding checks (most beneficial for a group).

I'm happy with the probability distribution this creates, of doable but not impossible for either party.

 

[Lonely Tylenol]

I think that the math answer is good if you are willing to do it. I think that the Take 10 answer is not a good idea since the guards are not benefiting from having each them getting a check which is one of the value of having multiple guards in one area.

So why does standing near another guard make someone better at listening?

The benefit to multiple guards is primarily that if an alarm is raised, there is enough manpower to deal with the problem, as well as the benefit of being able to scan a larger area simultaneously. If you want your guards to be able to hear a sneaky rogue nearby, you need to hire more skilled guards, or ward the place with Alarm spells.

I agree with Auraseer--if they're just regular guards who don't know something's fishy, they'll be taking 10. If theyre on alert, figure out what they need to roll to succeed and roll as many dice as you have guards. If you clear the target number, they notice.

Well, it's probably more trouble than it's worth, but you could just use the multiplicative property of probabilities. For example, if a character has a 50% of success on a Spot check (Spot +5, DC 15) and he needed to make 5 spot checks, his chance of succeeding on ALL of them would be:

50% ^ 5, or .5 * .5 * .5 * .5 * .5

Which means, for those for whom probability math is arcane, that the probability of succeeding on at least one would be equal to the 1-(the chance of failing on all of them).

So if your chance of failure is 50%, for five checks the chance of failing on all of them would be 50%^5, or 1/32 (about 3%). So the chance of succeeding on at least one is 97%. If your chance of failure is 75%, the chance of succeeding on at least one of five tries is about 76%. If the chance of failure is 80%, the chance of getting one is about 67%, etc.

So, if you want to account statistically for multiple guards making multiple rolls, you just raise the probability of failure to the power of the number of guards, subtract from one, and that's your percent chance. Not likely to map well to a d20, but you could roll percentile dice.

 

[Silveras]

Mathematically, Dr. Awkward is correct; the chance you are looking for is for ALL of them to fail, which becomes vanishingly small the more there are to check for.

However, for guards specifically, you might find the Vigilance statistic from CityWorks helpful (one of FFG's Legends & Lairs books). In it, city watch units are given 2 useful stats: Vigilance and Integrity.

Vigilance is used as a static DC for Characters to roll their Hide and Move Silently checks against, instead of an opposed roll. The base is determined by training (Class & level), with additional factors of pay level, morale, and some circumstance modifiers for the area.

Training
Rabble are base 5, Poor are base 10, Average are base 15, Good are 20, and Elite are 25.

Modifiers
Under/Overpaid is -5/+5, Poor/High morale is -5/+5, Wartime is +5, Low/High population are -2/+2.

So, an average unit of guards in average circumstances would be:
Base 15 + 0 (average pay) + 0 (average morale) + 0 (average activity/population in the area) = DC 15 to Hide or Move Silently

while an elite unit of well-paid guards stationed at a secure facility in a busy part of a town at war would be:
Base 25 + 5 (overpaid) + 5 (high morale) + 5 (war status) + 2 (busy area) = 42

Integrity works similarly, as a DC for bribery attempts.

 

[Storyteller01]

The benefit to multiple guards is primarily that if an alarm is raised, there is enough manpower to deal with the problem, as well as the benefit of being able to scan a larger area simultaneously. If you want your guards to be able to hear a sneaky rogue nearby, you need to hire more skilled guards, or ward the place with Alarm spells.

Also remember, having more guards means having to works around a smaller vector of entry. Two sets of eyes=double the area covered for Spot checks. Two sets of ears=a greater chance of hearing something. doesn't improve my hearing,but it ups the odds that SOMEONE will hear something...

However, I agree that if the guards are facing an everyday situation (not on full alert) then taking 10 is a good course. It's too mentally taxing and time consuming to question everything you see without any real justification. I'd also say add a +2 for every 2 guards, or 3 if there is a larger group (sports talk tends to override listening).

maybe you can do a single roll for the group, then another roll as needed. The first roll would be to see if any of the gaurds become suspicious. If you succeed on that roll, move on. If you fail, roll all the guards checkand find out who saw what. If you succedd on that, then they saw something and ignored it, if you fail...