D&D 5E Applying advantage to passive Perception


Great Old One
That's not how I would rule it. Dim light only imposes disadvantage on Perception checks that rely on sight. I wouldn't have that disadvantage cancel out the advantage on Perception checks that rely on hearing. So I would say that the owl might be able to hear something without being able to see it.

Maybe I was not clear (because I wrongly mentioned smell instead of hearing in the post), but it's exactly what I meant.

(I'm willing to be nuanced about Perception -- treating sight, sound and smell as separate things.)

So am I, just made a switch between smell and sound in the post.

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OK. So I still find it worthwhile (for me) to adjust a monster's statblock. The owl's would read "passive Perception 13 (18 w/ sights and sounds)". Makes it easier for me to remember the Keen Senses trait on the fly.


Great Old One
OK. So I still find it worthwhile (for me) to adjust a monster's statblock. The owl's would read "passive Perception 13 (18 w/ sights and sounds)". Makes it easier for me to remember the Keen Senses trait on the fly.
If it works for you, it's fine, it's just that I don't modify standard statblocks, I get them straight from DDB, and when I do a customised monster, it is still using the same formalism, but if it works best for you, great, and the advice might be useful to other DMs.


According to the rules for passive checks (PHB, p 175), having advantage on a check translates to a +5 bonus to the corresponding passive score.

Lots of monsters have Keen Senses, which grant them advantage on Perception checks under certain circumstances. Something I've done ever since the early days of 5e is make a note of this in monster statblocks.

For instance, a wolf has Keen Hearing and Smell, granting them advantage on Perception checks that rely on hearing or smell. By default, a wolf's passive Perception score is 13. Using the above noted rule, their passive Perception score would increase to 18 for the purposes of hearing or smelling. I make it so the Senses line in their statblock reads "passive Perception 13 (18 w/ sounds and scents)". I do this for all monsters / NPCs with a variation on the Keen Senses trait.

I'm just curious to know if anyone else does this, or am I the only one?
I do use the +5, but I do not write it dowm. If the perception could utilize the listed 'keen' sense the passive perception rises by 5.

My full process is follows when someone is hiding and I want to determine if the 'enemy' will detect them:

1.) Check to see if they have the conditions to maintain the hidden status (no direct and clear line of sight unless target is distracted, etc...)
2.) Determine passive perception.
3.) Apply modifies, such as advantage or disadvantage (but also circumstantial modifiers as well - I give bonuses for distance, for example).
4.) Check - does stealth exceed modified passive perception? If no, they are detected. If yes, go on.
5.) Determine if the observer is searching, inactive, active or distracted.
6.) A searching observer is actively trying to be perceptive, such as a guard that is doing their duty. They get a perception roll to see if they can improve upon their passive perception.
7.) An inactive observer is one that is not trying to be observant, such as a guard that is on watch, but they're bored and not great guards. Generally speaking, they're not trying to be observant, but they're not actively doing anything else, either. They get to roll perception to beat their passive perception, but I apply disadvantage to that role. Note that this gives them about a 1 in 4 chance of beating their passive perception.
8.) An active observer is one that is not trying to be observant and is actively doing something else with their action. This could be dashing (moving at 'full speed'), fighting, spellcasting, or something else. They get no perception roll - they are reliant upon their passive perception.
9.) A distracted observer is one that had their attention intentionally drawn away by someone else. They also get no perception roll and are reliant upon their passive perception - effectively being in the same boat as an active observer - but they had disadvantage on that passive perception (-5). Additionally, you do not automatically lose hidden against these observers if there is line of sight.


Great Old One
It's an interesting checklist, and I probably do it more or less consciously, just pointing out a few things:
  • There is the question as to whether the someone is hiding or not. Usually when checking this, that's the case, but they still need to have rolled for stealth at some point in the past. Even then, I sometimes use Passive Stealth, which is just how discreet someone is in general. For example scouting from afar, an orc might see that there are 4 noisy adventurers around a campfire, but might miss the rogue, naturally stealthy, in drab colours and avoiding light as a matter of reflexes.
  • You are absolutely right about the distance modifier. It's not something that the core 5e rule does or even support, but a DM at our tables just had us spotted by Winter Wolves from across a 100 meters chasm as if we had been right next to them, and it is a problem for verisimilitude, at least IMHO.
  • Searching observers are something a bit more for me than a guard doing his duty, it's someone actively searching and who would be using his action to search if he was in combat. I know the distinction that you are making there, but I would think it has to be a bit stronger than this for me.
  • I use automatic success and failure a lot, and passives as much as possible.
  • When someone rolls for stealth, he does so without seeing the result himself (hidden roll), that way he does not use the result to see whether to take risks or not, he always thinks that is is good.

I'd like to propose an alternate setup to better explain my reasoning for a dog granting advantage on passive perception for standing watch.

1. A single character is standing watch with a PP of 14. A band of goblins is sneaking up on the cam and the GM has decided the goblins have a 15 stealth. They elude the sentry and surprise the party.

2. The next day, to avoid getting bushwhacked again the party decides to post an extra watchman. Now they have TWO characters with a PP of 14 guarding. Same goblins sneak up, get a 15 again, and once again bushwhack the party.

3. The next day the party KNOWS the goblins are going to surprise them, so all 8 of them (who all have a PP of 14) stand watch. Goblins once again gat a 15 and sneak up for the third time successfully.

The existing rules try to accommodate this ridiculous situation from happening by allowing combinations of characters to improve a passive skill. Two ment with a 14PP on watch should always be better than one man with a 14PP on watch. Moreso with 6 people on watch.

This is why, out of rounds, I think it's fair to allow a wolf and a man to combine for a + to Passive Perception. I wouldnt have an issue with houseruling the modifier (I think the rangers PROF bonus is a better number here) but I think there should be a tangible one.

The dog already has advantage on Wisdom (Perception) checks that rely on smell or hearing - per the rules, that's +5 (so an 18) that the dog will perhaps smell or hear the goblins sneaking up. Woof!

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