Perception vs Investigation checks

Post date: Mar 06, 2017 7:50:52 PM

Relevant Skill & Feat descriptions

Passive Checks: A passive check is a special kind of ability 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.

Here’s how to determine a character’s total for a passive check:

• 10 + all modifiers that normally apply to the check

• If the character has advantage on the check, add 5. For disadvantage, subtract 5. The game refers to a passive check total as a score.

For example, if a 1st-level character has a Wisdom of 15 and proficiency in Perception, he or she has a passive Wisdom (Perception) score of 14.

Perception: Your Wisdom (Perception) check lets you spot, hear, or otherwise detect the presence of something. It measures your general awareness of your surroundings and the keenness of your senses. For example, you might try to hear a conversation through a closed door, eavesdrop under an open window, or hear monsters moving stealthily in the forest. Or you might try to spot things that are obscured or easy to miss, whether they are orcs lying in ambush on a road, thugs hiding in the shadows of an alley, or candlelight under a closed secret door.

• Light obscurement (such as dim light, darkness with darkvision, patchy fog, or moderate foliage): Gives disadvantage on Perception checks relying on sight.

• Heavily obscured (such as darkness, opaque fog, or dense foliage): A creature effectively suffers from the blinded condition (but is not actually blinded) when trying to see something in that area.

Houserule (Not visible): If you cannot see a hidden target, but could potentially hear the target or notice signs of passage, you may make a Perception check with disadvantage.

• If you succeed on the 1st roll, you know there is a target in the area, but do not know his specific location.

• If you succeed at both rolls, you can pinpoint which square the target is located on.

Insight: Your Wisdom (Insight) check decides whether you can determine the true intentions of a creature, such as when searching out a lie or predicting someone’s next move. Doing so involves gleaning clues from body language, speech habits, and changes in mannerisms.

Investigation: When you look around for clues and make deductions based on those clues, you make an Intelligence (Investigation) check. You might deduce the location of a hidden object, discern from the appearance of a wound what kind of weapon dealt it, or determine the weakest point in a tunnel that could cause it to collapse. Poring through ancient scrolls in search of a hidden fragment of knowledge might also call for an Intelligence (Investigation) check.

Observant: Quick to notice details of your environment, you gain the following benefits: You have a +5 bonus to your passive Wisdom (Perception) and passive Intelligence (Investigation) scores.

Discussion

Perception: I find it useful to record everyone's passive Perception (PP) at the start of the game. I also note down unusual senses (such as a warlock's devil sight or a owl familiar's advantage on perception checks based off hearing).

During the adventure, if a description includes something that can be noticed by the heroes senses (such as a wind current, unusual coloring on the walls, scrapes on the floor, odd mechanical noises), then I give that information in the room description if passive perception is enough (giving the harder to notice info to the ones with high enough passive Perception).

• Active Perception (takes a action): I allow a character to make an active Perception roll if they seem to have unusual reason to (i.e. another character who has a high perception checks alerts them that there is invisible object in the area). A character who tries to do an active perception check every time that they enter a area is actually using a passive perception and isn't allowed a roll.

Insight: I also find it useful to record everyone's passive Insight (PI) at the start of the game.

Insight is the social equivalent of Perception and should be used (instead of Perception) in social interactions. It is used in situations where you might spot social behavior that is unusual.

• Examples: Notice someone spreading rumors about someone, intentionally make someone look bad socially, lie, trying to stall, trying to blend with a crowd.

Investigation: If a hero has the Observant feat, I also note down his passive Investigation (PInv) (normally characters don't get a passive investigation as it has to be a active skill).

If the special information about the room is more due to deductive reasoning (i.e. Sherlock Holmes details, trap function, mechanical device, determining the floor scrapes are due to a secret door) then the player must actively use Investigate on the area or object involved (unless the character has observant and a high enough passive investigation, in which case I give the information to them automatically).

Example of Play

Three heroes open a door into a library study room with nice rugs, a few chairs, bookcases, and lit wall sconces. The area description includes the following unusual information:

• Secret door behind bookcase (Investigation DC20). Scrapes on ceiling above bookcase (Perception DC15)

• Illusionary floor in one area of the room (Investigate DC15)

• A hidden Invisible stalker (Perception DC20 to notice invisible presence, DC25 to pinpoint)

The DM informs the party of the following:

• Human Fighter (Int12/Wis10, Observant feat PP15/PInv16):  Scrapes on ceiling above bookcase. Illusionary floor (one area of the rugs pattern seems to not match correctly and doesn't show wear marks).

• Elven Ranger (Int10/Wis16, PP15): Scrapes on ceiling above bookcase.

• Halfling Rogue (Int12/Wis12, PP11, Expertise Investigation +5): -

The fighter suggests the rogue check out the bookcase (with his help) and draws attention to the scrapes on the ceiling. The elven ranger decides there might be more to this room than meets the eye and looks for anything out of the ordinary.

• Human Fighter (Int12/Wis10, Observant feat PP15/PInv16): Uses the Aid action to give the rogue advantage on his investigation roll.

• Elven Ranger (Int10/Wis16, PP15): Uses a active +5 Perception check and perhaps notices a invisible creature in the room (or even its location if he rolls a natutral 20).

• Halfling Rogue (Int12/Wis12, PP11, Expertise Investigation +5): Investigates the bookcase with a +5 Investigate (advantage) and perhaps locates the secret door (along with the wall sconce used to open it)

If the invisible stalker is noticed, it loses its surprise round if it ends up attacking. As soon as it attacks, its no longer hidden and it's location is clear (although still invisible).