Consider the following scenario: The party enters a room that appears to be a dead end, but in fact has a secret door with a magical trap on it. While standing in the room, a member of the party casts Detect Magic to see if there's anything magical in the room.
Does the glow of the trap's magical aura allow them to automatically locate it, without the need for a perception check? If not, does it grant a bonus of any kind on the perception check?
After 3 rounds of study with the spell detect magic, the magic aura will be located (and it might be located on the second round if it's the only aura). Then the caster makes a Knowledge (arcana) skill check (DC 15 + spell level) to determine the spell's school then, if that check's successful, with 3 more rounds of concentration, the caster can make a Spellcraft skill check (DC 15 + spell level) to determine the properties of the magical trap (which I assume is a magic item as it's created using the feat Craft Wondrous Item).
While this will locate the trap and learn the trap's details, that specific trap's precise details could still remain unknown. Ask the GM. For example, the caster may learn that a magic trap is proximity-triggered, but the GM may rule that the caster does not learn the exact proximity that will trigger that magic trap. (This may be the line the GM draws between learning a traditional magic item's properties and learning a magical trap's properties.)
However, detect magic is blocked by "1 foot of stone, 1 inch of common metal, a thin sheet of lead, or 3 feet of wood or dirt," and a trap-maker familiar with magic should build traps knowing that, therefore in such a way that the traps avoid such quick-and-easy detection by what the maker knows is a cantrip or orison. (And, obviously, detect magic doesn't detect utterly mundane traps at all.)
I always assume if your going to place a magic trap you would include Magic Aura as part of the trap. It's an illusion of a different magic aura, or no aura at all. It specifically gives false info to detect magic. If I let it have an aura to detect I usually use magic circle or illusion magic to fake something that could be interesting but not immediately threatening, or if the area is obviously dangerous then it's alarm or arcane lock, things that are a pain but not dangerous. I mean when you make a magic trap its a spell with a magic trigger that has to be detection magic which is different from the triggered spell's school of magic, so adding another specific low level effect like a little illusion magic shouldn't be too much of a stretch. For me it comes down to the cost, speed, skill, and mentality of the caster, would they have taken the time to do the trap right and hide it from detect magic with that spell or not?
