3e SRD:Spot Skill
From D&D Wiki
|This material is published under the OGL|
The Spot skill is used primarily to detect characters or creatures who are hiding. Typically, Spot is opposed by the Hide check of the creature trying not to be seen. Sometimes a creature isn't intentionally hiding but is still difficult to see, so a successful Spot check is necessary to notice it.
A Spot check result of greater than 20 can generally let the character become aware of an invisible creature near the character (though the character can't actually see it).
Spot is also used to detect someone in disguise.
|Per 10 feet of distance||-1|
the character can make a Spot check every time the character has the opportunity to notice something in a reactive manner. As a full-round action, the character may attempt to spot something that the character failed to spot previously.