Since D&D 3rd Edition came along and unified the resolution system for most rolls to a “1d20 + modifiers, beat the target number (DC)” there’s been a small but occasionally vocal crowd that has wondered why perception-based checks end up rolled under Intelligence sometimes and Wisdom others. It creates some moments of confusion, and even in D&D 4e and 5e — as well as numerous d20-based off-shoots like Castles & Crusades — some clear moments in the rules where the designers just picked an ability score at random. This leads to a few strange corner cases where the Cleric or Wizard is a better trap-detector than the Rogue, and things along those lines.
There’s plenty of good justification for all of this, but in some ways, there is a certain elegance in divorcing Perception from other Ability Scores, and truly focusing it as a subsystem specific to dungeon-crawling situations. It changes how the players approach the game, as well as how their characters are optimized (or not) for the environment; in point of fact, it evens the playing field considerably in AD&D and its derivatives, and that may be something you want to port over to your game of choice.
Presented here is a d6-based Perception system easily portable into any D&D-esque game. There is an additional variant for rogue-like characters who want their own, slightly more granular set of modifiers.
Old-School Perception Check
A Perception Check is simply rolling 1d6, adding some modifiers, and seeing if you roll equal or higher than some number.
There are three situations that typically require Perception Checks:
- Finding hidden objects
- Determining surprise in an encounter
- Detecting traps
There are two levels of hiding an object, whether it be a door, treasure chest, mechanism, or item: concealed or secret. Note that both fall under the category of “hidden object” for the purposes of these rules.
- Concealed objects are not immediately visible — they might be behind a tapestry, statue, or book case — but aren’t being actively camouflaged, so all it takes is a single glance behind the thing obscuring it to notice “Hey! It’s a door!” or whatever the object is. In other words, it is something that is not immediately in view, but with even the slightest effort, will automatically be found.
- Secret objects aren’t just obstructed from view, but have had active steps taken to conceal their very nature, such as hidden levers or mechanisms to activate them, hidden seams and hinges, or camouflaged (magically or naturally) covers.
Typically, there are two ways to find things: passive perception and active perception. In most, passive perception is useless except for a few special circumstances like keen senses granted as a racial benefit or class ability. Therefore, detecting a concealed object is automatic if a character actively searches for it, while a secret object requires a Perception Check.
Passive perception to find hidden objects: impossible.
Racial Modifiers. Elves and half-elves may detect hidden objects with passive perception simply by passing within 10 feet of the object; they detect concealed objects on 4+ and secret objects on 6+.
Dwarves may notice hidden objects within 10 feet with passive perception as well, but only in cases where the concealment involves stonework: they detect new stone work and slides/shifting walls on 5+, and traps (see below) on 4+.
Active perception to find concealed objects: automatically successful.
Active perception to find secret objects: 6+
Racial Modifiers. Elves and half-elves receive a +1 when actively searching for secret objects.
Dwarves receive a +2 when actively searching for secret objects that are related to stonework.
Surprise & Ambushes
Determining surprise for an encounter is another form of the Perception Check.
Determining surprise: 3+ means your character is not surprised.
Class Modifiers. Rangers and monks receive a +1 bonus to check for surprise.
Rangers impose a -1 penalty on their opponents’ checks for surprise.
Racial Modifiers. Elves and halflings impose a -2 penalty on their opponent’s checks for surprise when they are being stealthy in natural surroundings.
Many monsters are noted as being especially stealthy or able to surprise their opponents more often (such as hobgoblins) due to the use of ambush tactics. Impose a -1 penalty to the Player Characters (and any other opponents) in these cases.
Encumbrance. In AD&D and many OSR games, a character’s encumbrance can affect their ability to surprise others. Consider giving especially light-travelling characters a chance to impose a penalty on their opponents of -1 to their checks, or if the party member is wearing heavy armor or carrying lots of gear, give their opponents a +1 to their check.
By their very nature, traps are meant to be hidden, and thus — like secret objects — cannot be discovered through passive perception, making them especially dangerous, or forcing a party to move very slowly and cautiously.
Active perception for traps: 6+
Class Modifiers. Rogues and Monks receive +1 to actively search for traps at 1st level, +2 at 5th level, +3 at 10th level, and +4 at 15th level. Assassins receive these bonuses at a different progression: +1 at 3rd level, +2 at 9th level, +3 at 12th level, and +4 at 18th level.
Racial Modifiers. Dwarves may detect stone-based traps using passive perception (within 10 feet) on 4+, and will notice new stone-work or sliding/shifting walls on 5+. When actively searching for traps, they receive a +1 bonus against stone-work traps.
Listening is always active: a character stops moving, remaining as still and silent as possible to identify sounds and their origin, often through doors or other barriers, but sometimes simply at the edge of a corridor.
In any case, listening is specifically for detecting noises beyond a barrier, or for actively determining if there is some otherwise incredibly quiet, barely audible noise and determining what it might be. If something is quiet but not actively trying to be concealed, or not beyond some type of barrier that would naturally muffle it completely, then it should be automatically heard by anyone taking the effort to listen for it.
Actively listening to detect noise: 6+
Class Modifiers. Rogues and Monks receive a +1 to listen checks at levels 3, 9, and 15. Assassins receive a +1 bonus to listen checks at levels 5, 12, and 18.
Racial Modifiers. Gnomes receive a +1 bonus to listen checks.
Variant: Granular Rogue Skills
Alternatively, classes that receive a bonus to detect traps and listen can instead roll a d20 when actively looking for traps.
Active search for traps, Monk and Rogue: roll 1d20, succeed on 17+. They then receive a bonus to this roll as follows: +1 per level up to level 12.
Active search for traps, Assassin: roll 1d20, succeed on 17+. They then receive a bonus to this roll as follows: starting at level 4, assassins receive +1 per level up to level 16.
In the original rules, certain races received a bonus to this roll at level 1.
- Dwarf +3
- Gnome +2
- Halfling +1
- Half-orc +1
Dwarves should still get the benefits noted above for finding stone-based traps, as well.
For listening, use these rules:
Listening, Monk and Rogue: roll 1d20, succeed on a 18+. They then receive a +1 bonus to this roll every two levels (+1 at level 3, +2 at level 5, etc.) capping out at +8 by level 17.
Listening, Assassin: roll 1d20, succeed on a 18+. They then receive a +1 bonus to this roll every two levels (+1 at level 3, +2 at level 5, etc.) capping out at +8 by level 17.
The following racial modifiers apply to both classes:
- Elf +1
- Gnome +2
- Halfling +1
- Half-orc +1
D20 Perception Checks
With little work, the d20-based “granular” Perception Checks for skilled characters could be applied to all characters, creating a much more 3e-style “d20 ability check vs. Difficulty Class” roll. Without tying the modifiers to an Ability Score, and setting the DCs at fairly predictably high numbers (18-20), simply apply any class- or racial-based modifiers to the roll and there’s no longer a worry of high-Wisdom Clerics being more generally “alert” than the Rogue, or other issues that might harm the immersion vs. mechanics factor.
Do you use a different set of rules for Perception Checks? Let us know in the comments!
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