[RPG] How to avoid the determinism of Passive Perception

dnd-5eskills

From this question,

Passive perception is exactly that, passive. It's what the PCs are always using when not actively searching for something and doesn't use a roll of the die.

However, being that it is a fixed value, it is deterministic. My party, for example, has passive perception scores of 20, 19, 16, 15, and 12. My issue is that, when building a map with traps, I'm basically determining who will see them and who won't (unless they actively look for traps). The PC with 20 passive perception will notice everything the others notice. However, I don't like this system, I'd prefer there to be some randomness in it.

  • I could ask the PCs to roll a Perception Check, but that alerts the players and there's always some meta-gaming associated with it (e.g., in the next few minutes, everyone is careful entering new rooms).
  • I could also just tell them to roll a d20, and I add each person's perception modifier behind the screen, but I hate unknown rolls.
  • I could also just roll for all of them, all behind the screen, but that makes me roll lots of dice a lot of times.
  • A friend suggested asking players to roll a small die (1d6, for example) and I'll add it (or subtract it) to passive perception, behind the screen. He argues that, since it is passive, there shouldn't be such a large range of values (1 to 20), and that a small die with negative values (like a d6 ranging from -2 to 3) fixes the issue. He also says that this allows the players to roll (less work for DM, more fun for them) and it is not a secret roll (not really a d20, so players just assume I'm taking things from random tables and what not).

So, TL;DR: what is the best way to use Passive Perception (or active Perception without triggering players) in a way that is not fully-deterministic?

Best Answer

Invert your perspective: Roll dice against passive perception!

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.

I propose the following process to address passive vs fixed DC situations:

  1. Convert the target DC to a bonus by subtracting 12 from it (DC 15 - 12 = +3 bonus).
  2. Roll a d20 and add the converted bonus against the passive score of the character.
  3. Determine success (If you roll less than or equal to a character's passive score, then the character succeeds).

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:

  • The players don't have to roll, so there's no playing around with metagaming (at least any further then when you roll a hidden die).
  • The number of dice you need to roll is fixed.
  • The probability curve isn't as intense as when five people roll perception.
  • Requires little work.

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.

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