combatdnd-5eskills
Scenario: Players are fighting an invisible beholder and its Antimagic Cone. One player, with high passive perception, wishes to check to see if they are being effected by the cone every five feet they move.
Question: How often can the PC check with their passive perception during combat?
Let's head back to the rules for what Perception actually does:
Perception. Your Wisdom (Perception) check lets you spot, hear, or otherwise detect the presence of something. It measures your general awareness of your surroundings and the keenness of your senses. For example, you might try to hear a conversation through a closed door, eavesdrop under an open window, or hear monsters moving stealthily in the forest. Or you might try to spot things that are obscured or easy to miss, whether they are orcs lying in ambush on a road, thugs hiding in the shadows of an alley, or candlelight under a closed secret door. (PHB p.178)
Finding a Hidden Object
When your character searches for a hidden object such as a secret door or a trap, the DM typically asks you to make a Wisdom (Perception) check. Such a check can be used to find hidden details or other information and clues that you might otherwise overlook.
In most cases, you need to describe where you are looking in order for the DM to determine your chance of success. For example, a key is hidden beneath a set of folded clothes in the top drawer of a bureau. If you tell the DM that you pace around the room, looking at the walls and furniture for clues, you have no chance of finding the key, regardless of your Wisdom (Perception) check result. You would have to specify that you were opening the drawers or searching the bureau in order to have any chance of success. (PHB p.178)
Passive perception is only mentioned in the context of:
You would be quite within bounds to rule that these are the only things it works for; from your list, it would not help them find "secrets" (except secret doors) among other things.
You don't need a skill check to see the sun or the floor or the clock tower; you just see them. Similarly, you don't need a perception check to see the orc unless he is hiding, however, see how not to be seen. Or to see the statue but maybe you do to notice the eyes are emeralds.
Notwithstanding, passive Wisdom (Perception) is of no use whatsoever if the object is totally obscured: treasure in a refuse pile, a trinket in a desk, a wand in a pocket etc. you have to actually go through the refuse pile, open the desk, feel in the pocket etc.; these all require active engagement; either active Wisdom (Perception) or Intelligence (Investigation) as you deem appropriate.
In addition, things that are lightly obscured give disadvantage on both passive and active checks; this includes darkvision or dim lighting. If something is outside the range of your bright light source then you are going to have to go in for a closer look.
If you are allowing passive Wisdom (Perception) to be used universally, your comment that "... on average they get much better results with their passive perception" is irrelevant. If their passive perception is high enough to see the "thing" then they have seen it and active perception does not enter into the matter. If it isn't, then active perception will only help if they roll better than their passive perception.
Helping someone look gives advantage on their active Wisdom (Perception) check; you can't do this with passive perception. Teaming the best Wisdom (Perception) people in the party with the worst more than doubles their effective perception.
High passive Wisdom (Perception) only helps the individual character in a surprise situation. See How does surprise work in D&D 5e?; the relevant part being:
Surprise is something that happens to creatures; it does not happen to "sides".
Surprise is a quality of a creature; it does not describe a relationship between two or more creatures.
Essentially, your high passive Wisdom (Perception) PCs will rarely be surprised; everyone else in the party will still be surprised
DM: "You see a secret door; there are markings on the floor indicating that part of the left wall pivots into the corridor on the right hand side."
Player: "Great! I open it!"
DM: "How?"
Need I say more?
Let's say you have a valuable locket that you decide is hidden in a book in the third drawer of the desk. This is totally obscured unless the character opens the drawer; it cannot be perceived. Lets say you assign a DC20 Wisdom (Perception) check to find it if the drawer is opened. Lets also assume there is a trap door under the rug; this is not totally obscured because there are signs that the rug has been moved; say DC25.
Player: "I look around the room"
DM: "There is a chair, a rug, a desk with 4 drawers and a statue." If the player has a passive Wisdom (Perception) of 25+ you would add "It looks like the rug has been lifted and repositioned several times."
Player: "I search the room"
DM: Active check - if they get 25+ tell them about the rug. Depending on how you play the game "search the room" may encompass "open the drawers" - it doesn't have to but if it doesn't your players need to be aware of how specific they have to be. If they open the drawers then check against their passive Wisdom (Perception) to find the locket. If they search the drawers then they get an active Wisdom (Perception).
However, if they say "I lift the rug" then they find the trap door. If they say "I take out every item in the drawers and shake it" then they find the locket - no checks are necessary because these have just become obvious.
As you rightly observe in your 3rd paragraph, looking at the character sheets and penalising the players for the choices they made is unfair. D&D is a game of limited resources: maximising one skill means that something else suffers (lots of things, usually). The "world" is already getting this advantage; don't Nerf the things they are good at.
However, these traps and secrets were hidden by somebody, you can roll for how well they did with each one. Intelligence (Deception) is probably most appropriate, advantage can probably be assumed unless they were in a hurry. This gives you variation with the DCs without penalising the players. Note that this is exactly how Dexterity (Stealth) works.
I agree that passive perception seems odd when you consider that it's a fixed number against a fixed number. There's no chance. There's a hack you can do, however, to randomly determine success without the usability issues that you described.
In your example, you have a large party with various passive perception scores: 20, 19, 16, 15, and 12. They come across a trap, which has a fixed DC to notice it. This DC is used when the characters actively seek it out.
Lets say that the trap's DC is 15. With your example, all but one of your players automatically notice the trap. There is no drama, no chance for failure.
The game is built on the concept of using dice to determine success. Static comparisons aren't very fun, so all we have to do is use the static DC to notice as the basis of a die roll.
Note: the amount subtracted from the DC is 12 to maintain the same probability of success as an active roll! Thanks, Josh Clark for correcting me.
So, with your example, convert your trap's DC of 15 to a +3 bonus, and then roll a d20. Lets suppose you roll a total of 19. Two of your players have noticed the trap.
This doesn't have the pitfalls of any of the supplied solutions in the question:
There are some ramifications, however, of this: the party is basically challenged once against the best character's passive score. This could be considered a bug or a feature depending on your perspective. If you consider it a bug, you could use a variation of the group check rules found in the DMG: roll for each player's passive perception, and only allow success if half or more of them pass the check.
In practice, I've found this system to be very quick and fluid, with the given caveat that you must have all of your players' characters' passive scores pre-recorded. This is a requirement for any usage of passive scores, so I don't consider it an important point with this.
This system isn't really that much different to players than using passive scores as supplied in the DMG, since the characters will be passively using their bonuses in either case. I'm honestly not certain that my players noticed the difference when I adopted this system. For me, however, I didn't have to feel like I was condemning my players to an automatic snafu because I set a DC high.
As a final note, this post was inspired by an article by the AngryGM. Credit where credit is due.
Best Answer
You can't make Passive perception checks. Passive perception is what you use when you don't roll any checks; it's the baseline enemies need to beat when trying to hide from you.
In the anti-magic cone situations, the player doesn't check anything. If the beholder is hidden (because its stealth check exceeded the player's passive perception) then the player will not be able to find it.
Whether or not the player detects walking into the anti-magic cone depends on whether something obvious happens when they step into it. For example, if they have a Ioun stone, then they will obviously notice the thing falling to the ground. This does not depend on Passive Perception. On the other hand, if they have no visible magical effects on them, they might not realize that they stepped into an anti-magic field at all.
If the player wants an extra chance of finding where the Beholder is, they can make an active Perception check. That allows them to roll a normal Perception check (not use their passive) but since it requires an Action, they can probably only do that once on their turn. And it still won't help them in finding out about the anti-magic field.