Asking for Perception
I don’t know why this bothers me as much as it does, but when a DM asks a player to roll a Perception check, I can’t help but feel they’re doing it wrong.
In 4th Edition, you have two ways of viewing the world around you: Active Perception and Passive Perception. When you’re just walking around, not paying attention to any one specific thing, that’s when Passive Perception comes in to play; the DM checks the DC to notice the thing-to-be-noticed against your Passive Perception score. If your score meets or exceeds the DC, then you notice the thing-to-be-noticed, whether you were looking for it or not.
On the other hand, if you walk into a room and want to know as much as you can by actively turning the place upside down (so to speak), then you roll an Active Perception check against the DC to find whatever may or may not be in the room. This represents you taking an active role in the discovery of your surroundings.
Here’s what the Compendium has to say about the issue:
The Perception skill encompasses perceiving things, most often by sight or sound. Make a Perception check to notice a clue, detect a secret door, find a trap, follow tracks, listen for sounds behind a closed door, or locate a hidden object.
In most situations, the DM uses passive Perception to determine if a creature notices things.
I realize the Compendium says “In most situations…” but that’s just to cover those times when the player is describing what they want to do without actually coming out and saying, “I would like to roll a Perception check.”
For example, if the character walks into a room and says, “I’m going to check the bed, dresser, wardrobe, and nightstand, taking care to look for secret compartments”—but he never says the words, “I want to roll a Perception check,” well then of course the DM’s going to ask for it. In all other instances, the DM should be checking against the character’s passive score.
Of course, DM’s can help prompt for the roll by giving the player a description and then adding, “but that’s all you can see without taking a closer look.”
For more discussion on this topic, visit the thread I made on EN World.