Can passive and active Perception DCs be different?

Question

In the starter set adventure (as far as I'm told), secret doors are described as DC15 passive and DC10 when actively looking.

However, I've also been told that different DCs for passive and active isn't RAW, and that different DC for the hidden doors is just an earlier bad iteration of the ruleset.

On page 178, on Finding a Hidden Object,

In most cases, you need to describe where you are looking in order for the DM to determine your chance of success.

I take this to mean that, regarding a secret tunnel behind the bookshelf, if a PC is checking out the bookshelf (trying to find a cool book to take spells from), the DC of noticing the tunnel would be a lot higher than if the PC said that he was checking behind all the books for secret levers or such. From there, my interpretation is that, for passive perception checks, the DC can also be a lot higher, since the PC is not looking at anything in particular.

So, do the rules support using different passive and active DCs? Don't focus too much on the example I gave, it was just a way to make things clearer, but elaborate on it if desired.

Answer 1

Yes, you can have different DCs for active and passive DCs.

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I can not find anything in the DMG or PHB that explicitly says that the DC must be the same for passive and active checks.

It is somewhat implied in a number of places in the DMG where it says thing similar to this:

DMG pg 120-121

A trap's description specifies the checks and DCs needed to detect it, disable it, or both. A character actively looking for a trap can attempt a wisom (Perception) check against the trap's DC. You can also compare teh DC to detect the trap with each character's passive Wisdom (Perception) score to determine whether anyone in the party notices the trap in passing.

The language implies a single DC for either check, but does not outright state it. The list of traps on the next few pages also have a single DC for active and passive checks, but do not outright state that you must make them the same.

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However, in the section of the DMG on determining DCs, we see the following:

DMG pg 238

It's your job to establish the Difficulty Class for an ability check or saving throw when a rule or an adventure doesn't give you one. Sometimes you'll even want to change such established DCs. When you do so, think of how difficult a task is and then pick the associated DC from the Typical DCs table.

This directly gives you the authority to set or change DCs. It is perfectly reasonable (and adds to verisimilitude) for a passive check to have a higher DC than an active one.

Additionally, DMG pg 104 says:

Concealed Doors

A concealed door is a normal door that is hidden from view. A secret door is carefully crafted to blend into its surrounding surface, whereas a concealed door is most often hidden by mundane means. It might be covered by a tapestry, covered with plaster, or (in the case of a concealed trapdoor) hidden under a rug. Normally, no ability check is required to find a concealed door. A character need only look in the right place or take the right steps to reveal the door. However, you can use the characters' passive Wisdom (Perception) scores to determine whether any of them notices tracks or signs of a tapestry or rug having been recently disturbed.

This is a situation where the active DC is 0, but the passive DC is >0.

Adding this to the fact that in the Lost Mine of Phandelver pg 20, it says:

Spotting a secret door from a distance of no more than 10 feet without actively searching for it requires a passive Wisdom (Perception) score of 15 or higher, whereas a character who takes the time to search the wall can find the secret door with a successful DC 10 Wisdom (Perception) check.

And we have a second source that says that we can set different active and passive DCs.

So yes, you can set different DCs for active and passive checks.

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Something not stated in the DMG, but considered common practice, is to reduce the DC for more explicit explanations of a goal. As an example, compare this:

Player: I check the room for anything of value

DM: Roll Investigation [DC 12 for small treasure, DC 16 for secret compartment]

Player: 13

DM: you find 4 GP worth of small coins in various drawers of the desk in the corner, and a finely crafted, ornamental dagger worth about 20 GP over the mantle of the Duke's bed.

with this:

Player: I check the desk for anything of value, especially looking for secret compartments

DM: Roll Investigation [DC 5 for small treasure, DC 8 for secret compartment]

Player: 11

DM: you find 4 GP worth of small coins in various drawers of the desk in the corner, and little else worth carrying out to sell.

DM: However, you also find a false bottom on one of the drawers. After opening it up, you find documents proving that the duke is the head of the assassination attempt, as well as a tiny opal worth about 20 GP.

The more precise your players are at explaining what they are trying to do, the more likely they are to find what they are looking for (assuming it exists), but the less likely they are to find things outside that explanation that might be more obvious.

Answer 2

Yes: DCs for passive and active Perception checks can be different

First of all, there is nothing in the rules that forbids you from doing this however much you want, in any circumstance. However, your players would probably want a good reason for you to do this, as it violates expectations. That being said, there is a RAW example where you actually must make the DCs different for passive and active checks.

Evidence of this is explicitly given on page 177 of the PHB.

Passive perception. When you hide, there's a chance someone will notice you even it they aren't searching. To determine whether such a creature notices you, the DM compares your Dexterity (Stealth) check with that creatures passive Wisdom (Perception) score, which equals 10+ the creature's Wisdom modifier, as well as any other bonuses or penalties. If the creature has advantage, add 5. For disadvantage, subtract 5.

(Second bold added for emphasis).

For example, if you were searching for a trap door, by sight, in a room where the walls were covered in vines, the trap door might be considered "lightly obscured", as defined in PHB page 183

In a lightly obscured area, such as dim light, patchy fog, or moderate foliage, creatures have disadvantage on Wisdom (Perception) checks that rely on sight.

Thus, the DC for an active search could be 10, but made with disadvantage. Meanwhile, if the PCs weren't actively looking for trap doors behind the vines, but were in the room for some other reason, they might notice the trap door if their passive perception was high enough. They still need to pass a 10 DC check to find the door, but since they have disadvantage on the check their passive perception is reduced by 5. Thus, they'd need a passive perception of 15 or higher to succeed. Thus, for all intents and purposes, the DC is different for the passive and active checks: 10 (with disadvantage) for active, and 15 (effectively) for passive.