Perception and Detection

In bright light, such as sunlight, creatures and objects can be observed clearly by anyone with average vision or better.

Areas in shadow or lit by weak light sources are in dim light. Creatures and objects in dim light have the concealed condition, unless the seeker has darkvision or low-light vision, or a precise sense other than vision.

A creature or object within darkness is hidden or undetected unless the seeker has darkvision or a precise sense other than vision. A creature without darkvision or another means of perceiving in darkness has the blinded condition while in darkness, though it might be able to see illuminated areas beyond the darkness. If a creature can see into an illuminated area, it can observe creatures within that illuminated area normally. After being in darkness, sudden exposure to bright light might make you dazzled for a short time, as determined by the GM.

Average vision is a precise sense—a sense that can be used to perceive the world in nuanced detail. The only way to target a creature without having drawbacks is to use a precise sense. You can usually detect a creature automatically with a precise sense unless that creature is hiding or obscured by the environment, in which case you can use the Seek basic action to better detect the creature.

Average hearing is an imprecise sense—it can't detect the full range of detail that a precise sense can. You can usually sense a creature automatically with an imprecise sense, but it has the hidden condition instead of the observed condition. It might be undetected by you if it's using Stealth or in an environment that distorts the sense, such as a noisy room in the case of hearing. In those cases, you have to use the Seek basic action to detect the creature. At best, an imprecise sense can be used to make an undetected creature (or one you didn't even know was there) merely hidden—it can't make the creature observed.

A character also has many vague senses—ones that can alert you that something is there but aren't useful for zeroing in on it to determine exactly what it is. The most useful of these for a typical character is the sense of smell. At best, a vague sense can be used to detect the presence of an unnoticed creature, making it undetected. Even then, the vague sense isn't sufficient to make the creature hidden or observed.
When one creature might detect another, the GM almost always uses the most precise sense available.

A creature with darkvision or greater darkvision can see perfectly well in areas of darkness and dim light, though such vision is in black and white only. Some forms of magical darkness, such as a 4th-rank darkness spell, block normal darkvision. A creature with greater darkvision, however, can see through even these forms of magical darkness.

A creature with low-light vision can see in dim light as though it were bright light, so it ignores the concealed condition due to dim light.

Scent involves sensing creatures or objects by smell, and is usually a vague sense. The range is listed in the ability, and it functions only if the creature or object being detected emits an aroma. If a creature emits a heavy aroma or is upwind, the GM can double or even triple the range of scent abilities used to detect that creature, and the GM can reduce the range if a creature is downwind.

Tremorsense allows a creature to feel the vibrations through a solid surface caused by movement. It's usually an imprecise sense with a limited range (listed in the ability). Tremorsense functions only if the detecting creature is on the same surface as the subject, and only if the subject is moving along (or burrowing through) the surface.

In most circumstances, you can sense creatures without difficulty and target them normally. Creatures in this state are observed. Observing requires a precise sense, which for most creatures means sight. If you can't observe the creature, it's either hidden, undetected, or unnoticed, and you'll need to factor in the targeting restrictions. Even if a creature is observed, it might still be concealed.

A creature that's hidden is only barely perceptible. You only know what space it occupies. Perhaps the creature just used the Hide action. Your target might be behind some obstruction, where you can see some movement but can't determine an exact location. Maybe you've been blinded or the creature is invisible, but you used the Seek basic action to determine its general location based on hearing alone. Regardless of the specifics, you're off-guard to a hidden creature.
When targeting a hidden creature, before you roll to determine your effect, you must attempt a DC 11 flat check (in the sidebar). If you fail, you don't affect the creature, though the actions you used are still expended—as well as any spell slots, costs, and other resources. You remain off-guard to the creature, whether you successfully target it or not.

If a creature is undetected, you don't know what space it occupies and you're off-guard to it. The Seek basic action can help you find an undetected creature, usually making it hidden from you instead of undetected. If a creature is undetected, that doesn't mean you're unaware of its presence—you might suspect an undetected creature is nearby. The unnoticed condition covers creatures you're unaware of.
Targeting an undetected creature is difficult. If you suspect there's a creature around, you can pick a square and attempt an attack. This works like targeting a hidden creature, but the flat check and attack roll are both rolled in secret by the GM. The GM won't tell you why you missed—whether it was due to failing the flat check, rolling an insufficient attack roll, or choosing the wrong square. The GM might allow you to try targeting an undetected creature with some spells or other abilities in a similar fashion. Undetected creatures are subject to area effects normally.
For instance, suppose an enemy witchwarper cast invisibility and then Sneaked away. You suspect that with the witchwarper's Speed of 25 feet, they probably moved 15 feet toward an open door. You move up and attack a space 15 feet from where the witchwarper started and directly on the path to the door. The GM secretly rolls an attack roll and flat check, but they know that you weren't quite correct—your foe was actually in the adjacent space! The GM tells you that you missed, so you decide to make your next attack on the adjacent space, just in case. This time, it's the right space, and the GM's secret attack roll and flat check both succeed, so you hit!

If you have no idea a creature is even present, that creature is unnoticed by you. A creature that's undetected might also be unnoticed. This condition usually matters for abilities that can be used only against targets totally unaware of your presence.

A concealed creature is in mist, within dim light, or amid something else that obscures sight but isn't a physical barrier. When you target a creature that's concealed from you, you must attempt a DC 5 flat check (in the sidebar) before you roll to determine your effect. If you fail, you don't affect the target. The concealed condition doesn't change which of the main categories of detection apply. A creature in a light fog bank is still observed even though it's concealed.

A creature with the invisible condition (by way of an invisibility spell, for example) is automatically undetected to any creatures relying on sight as their only precise sense. Precise senses other than sight ignore the invisible condition. You can Seek to attempt to figure out an invisible creature's location, making it only hidden from you. This lasts until the invisible creature successfully uses Sneak to become undetected again. If you're already observing a creature when it becomes invisible, it starts out hidden since you know where it was, though it can then Sneak to become undetected.
Other effects might partially foil invisibility. For instance, if you were tracking an invisible creature's footprints through the snow, the footprints would make it hidden. Throwing a net over an invisible creature would make it observed but concealed for as long as the net is on it.