Maximum Perception Distance Underground?


Rules Questions


The rules give pretty clear examples of when your characters should roll Perception checks to detect enemies in various terrains. For example, sparse forest is 3d6x10 feet, medium forest is 2d8x10 feet, and dense forest is 2d6x10 feet.

But what about underground? If you're in a cave system, at what point do you start to roll for detecting enemies with Perception? Some characters have 60 ft. darkvision, some have 40 ft. with a light source, others have 80 ft. with low light vision from that same source, but all of them might hear an enemy at a fairly long distance.

Are there any guidelines or rules for this?


I can't find any Pathfinder rules for this. Maybe earlier editions had something you could use?


1 person marked this as a favorite.

Nothing that I can find. I could really use some help here.

Barring anyone having any clue what rule to use, my backup plan is to have both the party and the monsters roll their Perception checks to hear each other and the highest result is the distance x10 ft. that the encounter begins at. I really don't know if this is the correct way to do it, though.

Are their any guidelines in adventure paths that have underground caves, for example, that give an idea of what to do here?


JDLPF wrote:


Barring anyone having any clue what rule to use, my backup plan is to have both the party and the monsters roll their Perception checks to hear each other and the highest result is the distance x10 ft. that the encounter begins at. I really don't know if this is the correct way to do it, though.

That is pretty much my default. Just take away the lowest stealth roll of the opposing party before comparing if either or both are sneaking. It works quite well.


What's interesting to note is that the Perception DC for hearing a creature walking without Stealth is actually DC 10 per the Perception skill. A character in heavy armour can easily get below this with a poor to average Stealth roll, so it might be to their advantage not to use Stealth.

Of course, we could assume that this actually represents a passive Stealth check by an average creature with no modifiers, i.e. a Take 10 with a Stealth +0 modifier. But you know what they say about making assumptions.


Pathfinder Roleplaying Game Superscriber; Pathfinder Starfinder Roleplaying Game Subscriber

What would be the point? Most Perception distances will be limited by light sources, vision ranges, or solid rock walls and twisting tunnels.

Even if you're going by sound, many sounds can travel through miles and miles through a complicated tunnel system, even echoing and changing directions on you. In short, just because you hear it doesn't mean it's anywhere near you, or in the direction you think, so...what would be the point? Knowing something is there, but not knowing if it's up ahead or two miles away in another vault that you'll never discover, isn't really going to help you much.


The point is that combat shouldn't automatically begin at 60 ft. every time. A character with a high Perception can likely hear the approach of a group of enemies far sooner than they will see them. An extra round before combat lets characters draw weapons, drink potions or cast defensive spells.

I'd challenge you to show rules that support sound travelling miles through complicated tunnel systems. The entire point of this topic is that there are no rules for underground terrain Perception distance. Failing this, Perception rules apply, which would impose a +2 DC increase for unfavourable conditions, or an extra 20 ft. closer than average. For areas that let sound travel long distance however, such as Mountain terrain, the DC for Perception checks is actually +1 per 20 ft., meaning it's easier, not harder, to hear enemies approaching.

Solid rock walls only pose a problem if they're between the source of the sound and the character performing a Perception check. In an open cavern or a straight section of tunnel, these don't apply.

Since there's no official rules I'll just have to make up my own method, I suppose.


I used this for a forest intensive campaign, but it is entirely applicable to underground.

I took the stealth and perception scores from the enemies and the PCs, and then behind the screen took ten for both parties for perception. I then took a ten for both parties for stealth, or a zero if they were moving without any extra attention to be careful (making time down a major road, or hustling with no regard for stealth in the forest). The difference between the highest perception and the lowest stealth times ten was the distance that one party noticed the other. From there just add any circumstance bonuses you want. One party in dense undergrowth, plus four to stealth for a free forty feet. In your case, maybe add a minus five to perception for every bend in the tunnel. Almost forgot, you need to make up a stealth penalty for large groups.

I thought players would be against having me take ten for them behind their backs, but they really liked how organic and smooth it played. It would get boring soon if they kept on encountering the same enemy at the same distance, but with varied enemies it had lots of variety. Eg. You notice a goblin warband on the other side of this 200 ft wide valley, they haven't noticed the party. Or you just notice a wolf pack stalking the party as they are thirty feet away and closing in, roll initiative.


Not sure if this is rules or not, but here goes:

1) You cannot notice if there is no line of sight (LoS) to the other party.
2) Once the parties come into LoS, roll perception w/penalties as appropriate, and oppose with stealth as appropriate.
3) Determine result
3a) If both succeed, then both discover each other at the same time.
3b) If one succeeds, then that party can ambush or prepare for attack upon the other.
3c) If both miss, determine minimum miss and multiply by 10'. That is the additional distance closed before one party spots the other. [If both missed by the same about, they both spot each other at the same time.]

For a suggestion, if the LoS distance is greater than the vision limit, add a circumstance penalty of -10 to the roll representing using sound vs. sight.

As to hearing something and knowing someone is there, sure you know that someone exists nearby, but not where. Thus you don't know where to aim or otherwise attack. The only clue is the available directions that the location provides. You do not know which one the sound comes from.

/cevah


Pathfinder Roleplaying Game Superscriber; Pathfinder Starfinder Roleplaying Game Subscriber

Also, you can't ready actions to ambush until initiative is rolled anyways.


Perception modifiers on the perception check:
+1/10 ft of distance
+10/ft of thickness for a wall.
+2/-2 depending on unfavorable or favorable conditions.

At some distance, it is literally impossible to pass the roll (which yes- does make obvious jokes like "how do you see the sun?"; works well enough at the small scale). Work backwords from the highest perception check of the group for the point where they even have a chance to notice anything.

It isn't that hard. The most annoying part is just doing the math on the cut off line for each encounter.

Community / Forums / Pathfinder / Pathfinder First Edition / Rules Questions / Maximum Perception Distance Underground? All Messageboards

Want to post a reply? Sign in.