[RPG] How to use Passive Perception to have some characters notice parts of the environment


I'm new to DM'ing and have an issue I'm not sure how to deal with. The situation is this: It's pitch black outside and the PC is walking, with a lantern in hand, toward a building. A bird is perched atop the building, watching the PC. The bird is not attempting to hide in any way, but it's also not moving/squawking/drawing attention to itself.

I'm trying to figure out if the PC perceives the bird. If I blatantly ask the PC to roll a perception check, he'll realize there's something worth perceiving and just sit out there rolling until he sees the bird.

The question is, how do I roll against the PC's passive perception? This might seem exceptionally basic for experienced GMs, but I really don't know the mechanics of it. The PC has a passive perception of 17. Do I just roll a d20 against that with no bonuses? That seems too simple. The bird has no stats.

Any advice is appreciated. Thanks.

Best Answer

In and of itself, a bird on a roof is not something out of the ordinary, and not something that would (or should) alarm a character.

I assume from the fact that you are asking the question, that by noticing the bird, and divining its purpose, the character can gain some advantage in the near future.

So to me, this isn't even a perception question, but an insight one - I would let the bird be seen, almost automatically, but only address its significance if the PC passes a passive (or active) insight check.

I would ask the player if they are keeping an eye out for trouble or anything else in particular. If they claim to be, ask for details of what they are looking for, and then give answers appropriate to the questions that are asked.

DM: You proceed down the path towards the building. The light of your lantern illuminates the way ahead, but darkness pervades on either side of you. Do you make right for the building, or do you want to play it safe a study your surroundings?

PC: Play it safe of course. What do I see?

DM: Well, there are some trees on your right. You hear the rustle of what might be wings of a small bird pass overhead. Are you looking for anything in particular?

PC: Well, am I sure the noise is just a bird and not something bigger? Do I see or hear anything threatening?

DM: You're not totally sure about the sound, but you don't see or hear anything threatening.


If your players are going to feel betrayed when the significance of the bird is sprung on them, have them hear a bird call as well as the bird above, and then if they ask about birds, let them see the one on the roof, and maybe another in a tree.

If your players don't go for the idea of player skill (embodied here by the need for the players to divine that birds are significant), then a similar scene can be played out, bringing passive insight (or perception) into play by giving out details if their passive score beats a medium or high difficulty for their level.

Picture a suspenseful scene in a film - as the viewer you would expect to be aware of the birds before they are meaningful, but you would either not expect to know the role they have to play, or not expect to know which bird it is you need to focus on unless you have already learned the significance of birds.

As for what to compare the PC's active or passive perception or insight against, the Rules Compendium p126 has the difficulty class by level chart.

I would suggest that this is medium or hard to detect (as significant) for a low level character - so I would pick hard for level 5, which is a target number of 22.