Nail
First Post
The only problem with that is you might come into the "I don't move unless I check this square for a trap" problem.
I'd suggest one perception check per room.
Sure. One roll per 5 foot square is dumb, and I think we all know that.
It might be nice to do it like this: Use the passive perception check to recognize "something is amiss", and an active check (or revised Skill Challenge) to detect the trap itself.
Of course, some traps are much cooler after the PCs know they are there, so we can save the "auto-detect" for that.