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 is 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.

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 is 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.