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5e gamers who own the Player’s Handbook (PHB) tend to overlook the details of how passive perception works. Properly used, it can speed up your game, cut down on the monotony of constant active perception checks, and maintain the drama of ambushes and avoiding detection.

So, bluntly speaking, what is passive perception?

Passive perception is a character’s ability to notice what’s happening around them without actively examining their surroundings. You calculate your score by adding 10 to their perception modifier, which is their Wisdom modifier plus their proficiency bonus if proficient. 

If you can see, smell, hear, taste, or feel it while not actively looking for it, they use their passive perception. If you don’t use it all of the time, though, what’s the alternative?

When to use Passive Vs. Active?

The PHB is pretty clear on this. If a PC is actively trying to do something, then their player should make a skill check. Otherwise, the Dungeon Master (DM) uses their passive score (PHB pg. 175). 

Regarding perception, DMs should only prompt a check if a player said something like:

• “My character’s keeping an eye out for danger”, or
• “We’ll set up a watch so that there’s always someone on guard.”

If they haven’t, then their passive perception will have to do. 

A particularly lenient DM might prompt players upon first entering a dangerous space by asking them how they proceed. If they still don’t think to search for threats, then an ambush might need to catch them off guard.

Passive perception can also be used as a gatekeeper for active skill checks. 

For example, you could say that only someone with a passive perception of 14 or higher would notice that a barn’s hay floor has been piled a bit deeper in several spots. Those characters could then be prompted to make an active perception check and see the metal glint of a bear trap hidden in one of these piles. 

The player received free information (there are suspicious piles of hay), and also a chance to learn more if they succeed at an active skill check (traps are hidden in the piles).

As far as monsters & NPCs, my rule of thumb is to have all enemies in an area start by using their passive perception. 

Once the party has caused a disturbance—made a loud noise, got into a prolonged fight, set off an alarm, etc.—they all switch to making active perception checks. They’re on guard now. Don’t slip up again!

But how does this work once the players start getting sneaky?

How can you use Passive Perception with Stealth?

If a player wants to sneak, they must roll a stealth skill check. Anyone looking for them rolls an opposed perception check—the higher roll wins.

For a tie, Rules-as-written (RAW) say:

If a contest results in a tie, the situation remains the same as it was before the contest.

Player’s Handbook (PHB) Pg.174

To me, the above quote means that the stealthy character remains undetected, but they’d only barely be hidden.

Enemies that aren’t actively searching use their passive perception.

When my players want to creep through an area undetected, I usually only have them make a stealth check once.  The outcomes would go like this:

• If they rolled low, it’s instant combat. They knocked over a vase, and the orcs come out to investigate. Roll initiative. Now everyone’s on high alert–no more stealth. 
• If they rolled high, they could confidently move through the area. They’ll have a good time slipping by oblivious guards and snagging loot along the way. 
• If the roll’s mediocre, though, that’s the most fun of all! They can never be sure of themselves. They feel hidden, but are they? Any monster might be the one that finally catches them. They may have already been spotted and just don’t know it yet! 

That’s dramatic – and drama is engaging.

If a monster’s passive perception beats the party’s stealth roll very slightly, I’ll often opt for something subtler than outright combat. 

Maybe they’ll call a buddy over and say that they heard something. The players aren’t busted yet, but now they’ve got twice as many guards to sneak past. Alternatively, maybe the bad guy isn’t suspicious enough to send up an alarm, but he’s going to start keeping a closer watch on the shadows. 

Now he’s making active perception checks actively, and since his passive perception was already higher than the party’s check, that’s a dangerous situation! It’s become an even bigger problem for the players to handle – only now it has a ticking clock.

Even more dramatic!

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Other Ways to Incorporate Passive Skill Checks 

Perception is by far the most used passive skill check, but the Player’s Handbook makes it clear that all checks can be used this way. Here are some ideas for a DM looking to spice up their game with additional passive skill checks.

A PC with a high score in the following skills might:

• Arcana: Feel whenever there’s magic nearby.
• Deception: Tell a few lies in a conversation before they need to roll, supposing they’re not obvious ones.
• History & Religion: Always have vague knowledge on a relevant thing that they examine, no matter how low their roll was.
• Insight: Be good at reading a room or catching obvious lies.
• Intimidation: Shut down minor confrontations just by making their presence known.
• Investigation: Intuit how complex machines function or tell from scratches on the floor indicate that a bookcase might swing out to reveal a hidden passage.
• Nature: Recognize a monster, or it’s type, on sight.
• Survival: Avoid getting lost when traveling through swamps, jungles, or other backwoods.

How to Boost Your Passive Perception

Players who dislike being surprised have many options to increase their passive perception: 

• Having a high Wisdom score is the most obvious. 
• The observant feat increases your passive perception & investigation by 5. 
• Rogues & bards that are proficient in perception can choose to give that skill expertise–doubling their proficiency bonus.

A committed player could optimize their PC up to a passive perception score of 32! Now that’s what I call being alert.

Summary

Passive perception might seem useless at first glance, but used properly, it improves pacing, builds tension, and allows players to “fail forward” in dramatic and satisfying ways.

• Passive skill checks can be made for any skill in the same fashion as perception, allowing for a more tailored, interactive. For DMs, this may require writing down each player’s ability modifiers.
• Default to passive checks unless otherwise stated. If a character’s passive slightly beats the opposing skill, then approach it subtly rather. Example: passive perception beats the stealth check by a couple points – they investigate instead of sounding the alarm.
• Boosting ability scores, magic items, and class traits (bards and rogues) can help boost passive perception.

No considerate DM should exclude it from their toolkit.