The player describes how the character looks for the trap, the precautions he takes, etc.
The DM describes what he finds.
If the player thinks a crack or wire or something is a trap, he describes how he disarms or bypasses it.
At that point the DM might call for a DEX check....
Then the NPC is on the fence.
I figured cut to the chase.
I was actually referring to finding the trip wire in the first place.
I see what you're saying though. The player describes what they're doing in exacting detail and the DM decides what happens as a result. I enjoy that kind of play as an occasional "zoom in" on the action, like the players putting their heads together to suss out the workings of an ancient Titan device, but I certainly wouldn't want it for every 5 feet of corridor. I realize some groups used SOP, wherein they only needed to describe what they were doing in unusual circumstances but... not for me. I think that even if a character is keeping an eye out for trip lines (and/or whatever) they might still trip up. Sometimes I just want to be able to roll some dice and move on, rather than being bogged down in an endless back and forth (hence why I felt 3.x was a vast improvement). Obviously though, if you and your group don't mind, more power to you.