[RPG] Should I use characters’ passive Perception scores or ask for an active Perception check to detect hiding enemies


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.

Best Answer

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)