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Perception and Stealth

Source Ultimate Intrigue pg. 187
Since Perception is the skill that determines what a character sees, hears, and senses in the game world, it is no wonder that it’s often considered the most important skill in the game. Stealth and Perception often oppose one another, and the two of them together can be difficult to adjudicate.

Active and Automatic Perception: There are two ways Perception checks happen in the game. The first way is automatic and reactive. Certain stimuli automatically call for a Perception check, such as a creature using Stealth (which calls for an opposed Perception check), or the sounds of combat or talking in the distance. The flip side is when a player actively calls for a Perception check because her PC is intentionally searching for something. This always takes at least a move action, but often takes significantly longer. The Core Rulebook doesn’t specify what area a PC can actively search, but for a given Perception check it should be no larger than a 10-foot-by-10-foot area, and often a smaller space if that area is cluttered. For instance, in an intrigue-based game, it is fairly common to look through a filing cabinet full of files. Though the cabinet itself might fill only a 5-foot-by-5-foot area, the number of files present could cause a search to take a particularly long time.

Precise and Imprecise Senses: Since Perception covers all senses, it is important to distinguish which of those senses count as observing a creature that is using Stealth. Some senses are more precise than others. Imprecise senses allow a creature to pinpoint the location of another creature, but they don’t allow for the use of targeted effects, and attacks against those creatures are subject to miss chances from concealment. A few examples of imprecise senses are hearing, scent, blindsense, and tremorsense. A sense is precise if it allows the creature to use targeted effects on creatures and objects it senses, and to attack enemies without suffering a miss chance from concealment. This includes vision, touch, blindsight, and lifesense. Precise senses allow the creature to pinpoint an enemy’s location. When a creature uses a precise sense to observe an enemy, that enemy is unable to use Stealth against the observer unless it creates a distraction first, or has a special ability allowing it to do so. Senses other than the listed ones count as precise or imprecise at the GM’s discretion. A creature might have a limited form of a sense that makes it too weak to count as precise, such as a beast with primitive eyes that has difficulty seeing a creature that isn’t moving.

Cover and Concealment for Stealth: The reason a character usually needs cover or concealment to use Stealth is tied to the fact that characters can’t use Stealth while being observed. A sneaking character needs to avoid all of an opponent’s precise senses in order to use Stealth, and for most creatures, that means vision. Effects such as blur and displacement, which leave a clear visual of the character within the perceiving character’s vision, aren’t sufficient to use Stealth, but a shadowy area or a curtain work nicely, for example. The hide in plain sight class ability allows a creature to use Stealth while being observed and thus avoids this whole situation. As the Core Rulebook mentions, a sneaking character can come out of cover or concealment during her turn, as long as she doesn’t end her turn where other characters are directly observing her.

States of Awareness: In general, there are four states of awareness that a creature can have with regard to another creature using Stealth.

Unaware: On one end of the spectrum, a sneaking creature can succeed at Stealth well enough that the other creature isn’t even aware that the creature is present. This state allows the sneaking creature to use abilities such as the vigilante’s startling appearance. The Stealth skill description in the Core Rulebook says that perceiving creatures that fail to beat a sneaking character’s Stealth check result are not aware of the sneaking character, but that is different from being totally unaware. This is also true of a creature that has previously been made aware of the creature’s presence or location (see below) but is currently unable to observe the sneaking creature. In those cases, the sneaking creature can’t use abilities such as startling presence.

Aware of Presence: The next state is when the perceiving creature is aware of the sneaking creature’s presence, though not of anything beyond that. This is the state that happens when an invisible creature attacks someone and then successfully uses Stealth so the perceiving creature doesn’t know where the attacker moved, or when a sniper succeeds at her Stealth check to snipe. A perceiving creature that becomes aware of a hidden creature’s presence will still be aware of its presence at least until the danger of the situation continues, if not longer (though memory-altering magic can change this).

Aware of Location: The next state is awareness of location. This happens when a perceiving character uses an imprecise sense, such as hearing or tremorsense, to discover what square a hidden or invisible creature inhabits.

Observing: The final state is when the perceiving character is able to directly observe the sneaking character with a precise sense, such as vision. This is generally the result when the perceiving character rolls higher on its opposed Perception check than the sneaking character’s Stealth result while also having line of sight to the sneaking character and the ability to see through any sort of invisibility or other tricks the sneaking character might be using.

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Perception and Stealth