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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?

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  • \$\begingroup\$ "locate it" for what purposes? Disabling it? Avoiding triggering it? Or just knowing where the fireball that's going to engulf will originate from? \$\endgroup\$ – Erik May 23 '16 at 13:56
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    \$\begingroup\$ @Erik For any purpose. If the purpose of detecting the trap would, for some reason, make a difference, then answers should cover all relevant cases. \$\endgroup\$ – Oblivious Sage May 23 '16 at 14:00
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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.)

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  • \$\begingroup\$ If the trap is magic, then you cannot block it behind the materials you mentioned, otherwise there would be no way to trigger the trap without adding mechanical elements. \$\endgroup\$ – Trisped May 23 '16 at 19:34
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    \$\begingroup\$ actually, using blocking materials is a great way to hide the trap AND make sure it works the way you want it to. Paint your alarm and fireball runes on a sheet of lead attached to the BACK of the door - it won't show up to detect magic from the hidden side, and then if someone DOES find it and goes through it, it will explode behind them. Who checks doors they've already walked through for traps? \$\endgroup\$ – gatherer818 May 23 '16 at 20:07
  • \$\begingroup\$ @Trisped I direct you to gather818's comment above for one such insidious example. Also, because of Pathfinder's combination of exacting yet vague trap rules, the GM needn't explain how a particular trap prevented the caster from finding a trap's magic aura, but a good GM would make such a method available also to the PCs if they investigated hard enough or possessed sufficient ranks in Craft (trapmaking) or whatever. \$\endgroup\$ – Hey I Can Chan May 23 '16 at 20:31
  • \$\begingroup\$ Yep, the mechanical element is the door (which swings open). Of course, that trap is technically 100% undetectable, so it depends on the kind of campaign the DM is running. \$\endgroup\$ – Trisped May 23 '16 at 23:55

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