ellestar said:
Ok, let me rephrase my question then: Can a wizard with detect magic find magic traps through detect magic? (eg. their exact location; "there's a magical symbol above the doorway") Or do they merely detect the presence of a magical aura in the room (or rather, in the area of effect of the spell)?
After three rounds of concentration on the same area, the wizard knows the location and strength of every magical effect in that particular 60' cone. At that point he can also make his Spellcraft check to determine the school of magic.
A party could theoretically use a permanent
detect magic to automatically spot magic traps, but it would be annoying and imperfect. The caster would need to study every chest, doorway, object, room, and 60' section of corridor for 3 rounds before anyone else approached, which would be slow and boring. It'd miss anything protected with
magic aura. Most importantly, it would give lots of false positives if there's any other magic operating in the place. (And in a D&D world, almost anywhere that adventurers go is bound to have magic operating.) If my party wasted a
dispel every time the wizard sensed magic, they would go through their entire daily spell allotment before lunchtime.
This is no more a problem than if the rogue tried to take 20 to search every square foot of corridor before stepping on it. Sure it's technically possible, but it'll take days for the party to get anything done. By the time they reach dungeon level two, the evil wizard on level five will have completed his dark ritual and taken over the world.