Should I use characters' passive Perception scores or ask for an active Perception check to detect hiding enemies?

Question

I'm DMing for a party that constantly says stuff like "We'll walk slowly and carefully," or "We'll look around as we walk, to make sure there's nothing threatening or out of the ordinary."

Say there's a monster hiding near the PCs (it makes a Stealth check and rolls a total of 14). All the PCs have a passive Perception lower than 14.

Given the above statement by the PCs, should I now ask for an active Perception check to see if they spot the monster hiding? Should I always ask for an active Perception check from now on, since they're always being careful?

On one hand, they did say they were being careful and looking at their surroundings. But on the other hand, I feel like that's already assumed, as a party of adventurers wouldn't just nonchalantly walk into a dungeon - therefore I feel like this is exactly what passive Perception is for.

Answer 1

You are the DM, so it's your job to decide

Regarding ability checks 5e no longer dictates the DM how to play. It provides the DM a toolbox instead. When, how and what tool (not) to use it's up to the DM now.

Passive checks are DM's tool that allows one not to roll for everything, hence speed up the game. You can use this tool or not to use, in the end of the day it's a matter of personal preference.

Generally speaking, DM are supposed to use passive check when (s)he wants to hide the roll result from players for any reason. See PHB page 175 (emphasis mine):

A passive check is a special kind of abilily check that doesn't involve any die rolls. Such a check can represent the average result for a task done repeatedly, such as searching for secret doors over and over again, or can be used when the DM wants to secretly determine whether the characters succeed at something without rolling dice, such as noticing a hidden monster.

It also looks weird when you ask players for a check but don't give any result. So, in your particular case you probably want to use active check in the beginning of an ambush, but passive check when there were no immediate consequences.

Keep in mind there is Observant feat that affects passive checks specifically. If one of the players has this feat, the feat would be nerfed if DM does not use passive checks.

It also worth mentioning, that opposed checks makes things easier for stronger side, especially when the difference is more than 5.

Beware of no-brainers

... party that constantly says stuff like we'll walk slowly and carefully, or we'll look around as we walk, to make sure there's nothing threatening or out of the ordinary

There might be a reason why players say this. Perhaps there was a precedent when players were caught on the spot and ambushed and the DM rationalized this as "you weren't paying attention". Now players always say things like "we do it carefully", because this let them avoid troubles.

The DM listen to this and no longer treat PCs as unprepared or at least asks for an ability check. This is pretty reasonable. The problem is, it's a no-brainer and no-brainers are bad design.

If walking "carefully" has no downside compared to just walking the normal way, then you should assume that's what everyone does all the time, and that's why they get passive Perception at all instead of just blundering right into danger. (thanks @MarkWells for summing up)

Answer 2

Don't ask when they are near the creature

Firstly you shouldn't just ask for rolls when something is hiding near by as even if they fail the players will know something is up.

You can get them to roll if each time they enter an area if they say something like "I have a look around before we go through the doorway." You could also treat it like a stealth roll where you get them to roll at the beginning and/or at regular intervals.

Active perception is exactly that, active. They have to be actively looking/listening for things. If the characters are carefully looking around everywhere they go that may be active. Passive perception is about noticing things when not expressly trying to such as a rumble in the background while they are walking along a road.

I would argue it is not the same situation when carefully exploring a dungeon as nonchalantly walking down a road so they shouldn't be judged the same way. If you think characters would be actively looking around in a dangerous situation then that is active, even if you consider it to be normal.

I'll also make the point that in D&D PC's often do nonchalantly walk around in dungeons especially at higher levels if they don't have a rogue.

Answer 3

You cannot be actively watching out ALL THE TIME

Passive perception is effectively keeping watch while still being able to do other things, it is the average of their attempts at keeping watch, and if they are going to be keeping watch at all times taking the average is the most sensible solution.

If they are always on the lookout there is no chance for you as a DM to say 'make a perception check' for x, y or z situation they get into, you just have to tell them what they see based on the earlier watch rolls, which isn't fun either.

Only roll an active perception check when something happens and the players stop whatever they are doing and look, such as when they peek out from behind a corner.

Answer 4

It's your call either way, and you don't need to directly allow this

As other answers have already pointed out, this is fundamentally your decision to make as DM for this game. As such, I'm not going to tell you which ruling you should make but instead list some items which bear on the decision either way:

• Players do not get to dictate when rolls happen, nor what those rolls are

You decide when to call for a roll, and what that roll should be. By saying that they're constantly making Perception checks, they are in essence telling you when to allow them to roll, and those instances just happen to be when there's something to perceive.

• Making a Perception check is a specific action, not a general condition

From the PHB section on the Perception skill:

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.

Emphasis mine. Players are supposed to use a Perception check like this more as the culmination of a specific action, and that is the major thing which differentiates the skill check from using the passive score. "I'm looking at, listening to, touching, tasting, and smelling everything in an effort to find anything at all" really doesn't fit that very well.

• The game includes passive scores so that they will be used

A weak counterargument, even setting Rule 0 aside, but this suggested approach makes all passive scores irrelevant through a trivial declaration. You don't have to use the passive scores in your game if you'd prefer not to, but if you grant this request there will be little reason for the characters not to be constantly savvy and prepared for anything that ever comes up.

• Making Perception checks may be time consuming

Passive perception is what's used when your mind is on some other task and you happen to notice something amiss. These players are indicating that they want to check everything for everything, which would naturally involve a great deal of careful, methodical examination of everything they come across.

There are a lot of situations where that flat-out isn't going to work, such as trying to escape from a dungeon under a time limit. In other situations it may be possible but not practical, like trying to beat another adventuring party to a treasure hoard. And the classic approach to stopping players from using time as an inexhaustible meta-resource is to have them risk random encounters while they putter around endlessly-- their slow pace could ultimately prove fatal.

The overarching point of this section is that players have made an argument (whatever you think of it) that their approach should grant them extra success against things like hiding enemies and traps. You can allow that or not, but the game itself doesn't need to leave that dominant strategy in place forever-- you can make nonstop Perception checks expensive for them, changing it from a game-dulling easy mode to an interesting decision they have to make in specific situations.

• Always using rolls can produce worse results than the passive checks, complicating the strategy and its narration

Passive scores always are what they are (never mind ASIs)-- they are a minimum of 5 (base 10, plus a -5 modifier from having an Ability score of 1), and having an Ability score of 1 is going to be rare for a PC. The more typical situation is going to be a passive perception greater than 7.

A consequence of that is that a player could potentially roll a result worse than their passive perception. This may not be a hugely likely or consequential situation in your game, but it's worth pointing out that your players won't necessarily get the benefits they're expecting, and could potentially miss some pretty big things in their zeal to notice absolutely everything. As DM, you can make that more likely in key situations.

• Players don't generally get to declare permanent advantages for themselves

This approach of constant examinations has the effect of making the game mechanically easier for the players, particularly if you do not add other constraints to balance it. Enemies that rely on stealth and ambushes will be automatically nerfed, possibly to the extent that you won't bother using them. Traps become less meaningful, and dungeon exploration less tense. And all because the players just announced that their characters were being super careful.

I love it when players come up with clever ideas, and they get to enjoy the benefits of their cleverness. But this argument of constant, focused attention is pretty weak and poorly structured. I doubt you'd allow it if a player said that, because their Fighter is so well trained with a sword he would be really careful during a fight and so should always get Advantage on attack rolls.

The character stats and dice rolls bridge the gap between what a player/character would like to do and what they are actually capable of doing.

Answer 5

1. Do you want to speed up the game by avoiding dice rolls?
2. How well are they hidden?
   DC levels well above the party passive perception would need an active roll, while a good roll would allow you give more detail prior to combat.

This is a good time to have a misdirection. They see the Gnolls but miss the spike trap in the floor or trigger a vision obscuring magic, or even flour, or a dust trap that is triggered as the party rushes in to be murderhobos.