Use this skill to notice and pick up on things. Discerning details—such as clearly hearing conversation or reading fine text—requires at least three degrees of success on the Perception check.
The "Discerning Details" concept should not be ignored. It can be easy to see Baron Bal
In general, you have a –1 circumstance penalty to Perception checks for every 10 feet between you and what you are trying to perceive. So hearing a noise from 50 feet away is a –5 modifier to your Perception check, for example.
The GM usually makes Perception checks secretly so you don’t know whether there was nothing to notice or you simply failed to notice it.
You can make Perception checks involving other sense types as well (see Powers for more on sense types). Noticing something obvious to a sense is DC 0. Less obvious things are DC 10 or so, hidden things DC 20 or more, and discerning details requires at least three degrees of success, as usual.
You can make a Perception check every time you have the opportunity to notice something new. As a move action, you can attempt to notice something you failed (or believe you failed) to notice previously.