Detect magic VS magical trap?


Rules Questions

Sczarni

Like the title says how exactly detect magic works with magical trap?

Do the sorcerer sense an aura of evocation around the archway or he knows that there is a maximise/empower fireball that gonna blow up if he step on that plate around the corner?

I did'nt found anything that adress that question neither in detect magic spell description nor in the trap section.

Thanx


By RAW detect magic would detect a magical trap.

Many GMs hand-wave this since it means a 0 level spell can defeat their CR 12 encounter. Other GMs simply have their traps' magical auras hidden from detect magic.


You can use lead or a non-detection spell as appropriate to hide magical auras.

Liberty's Edge

Pathfinder Companion Subscriber; Pathfinder Roleplaying Game Superscriber
Detect Magic wrote:


You detect magical auras. The amount of information revealed depends on how long you study a particular area or subject.

1st Round: Presence or absence of magical auras.

2nd Round: Number of different magical auras and the power of the most potent aura.

3rd Round: The strength and location of each aura. If the items or creatures bearing the auras are in line of sight, you can make Knowledge (arcana) skill checks to determine the school of magic involved in each. (Make one check per aura: DC 15 + spell level, or 15 + 1/2 caster level for a nonspell effect.) If the aura eminates from a magic item, you can attempt to identify its properties (see Spellcraft).

A magical trap is not a magical item (the need to have Craft wondrous items to build them notwithstanding) so you would only detect the spell aura.


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And many more just run it as is.

After casting Detect Magic, they will detect there's magic around. They will detect where the magical trap is after 3 rounds of studying. Assuming it's a normal magical trap (triggered by alarm), they will detect that abjuration. The fireball has not happened yet, so I see no reason for them to detect the evocation. You could always be nice to let them try to identify the trap as you would an item, and learn what it does.

But I think RAW, you would just detect the abjuration, or whatever else the trigger is.

Shadow Lodge

Luckily, if you are creative, or if you own some of the Grimtooth's Traps books (or ideally, both), there are mundane traps that absolutely humiliate the most powerful of magical traps.


Initially Detect magic would tell you there's magic somewhere in the 60' cone in front of the person detecting... not specificaly that it is on the doorway... this would include the fighter standing in front of him with the magic sword, and the potion on the rogue behind him, et al.

(GM's really should pay attention to this aspect of it, for those PC's that think they can just walk around detecting constantly without severely hindering their rate of progress and not standing in front the whole time.)

If they stand there staring at it for 3 rounds, then they'd know its location and strength, possibly school of magic.

Also, like most detection spells, it won't really work through a great deal of stone or other materials)

Magical Aura spell works for hiding your traps if you really need to, and can justify it being there.


In the case of the magical fireball trap listed above, unless the trap is shielded, a moderate aura of evocation would be detected.

It would be a rare adventurer who did not immediately say "Crap! Fireball trap!"

They wouldn't "know" it was a fireball, much less an empowered one, but they'd know something was likely to go boom.


Fairly simple trap that I came up with using 3 spells. It's on a 'sticky note' on my laptop:

Sticky Note wrote:

(Journal Entry) Forgot password to the Wall again trapped inside my own bedroom. Will have to wait till tomorrow to get out. Note to self, keep password behind bookshelf.

Removable wall panel with Fire Trap (DC 29 Perception/Disable DC; 20 Reflex). Parchement and chest inside wall panel.

Parchement says, "The password to the wall is EXPLOSIVE RUNES!" DC 19 Reflex.

Chest with Explosive Rune (Boom!) parchment on stuck to latch, Fire Trap on Chest, inside is caster’s spellbook, Fire Trap on book.

Firetrap doesn't harm the warded object, so the book doesn't burn. All spells have aura hidden.

Spells used, Fire Trap, Explosive Runes, Magic Aura. Detect Magic would not be able to use to find these traps.


If you are in a dungeon with magically treated walls it can be easier to hide a trap as well since most everything will detect as magic.


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Many of my dungeons are filled with diversionary auras and masked auras. My players learn quickly that detect magic is a zero level spell.

Dark Archive

Vaahama wrote:

Like the title says how exactly detect magic works with magical trap?

Do the sorcerer sense an aura of evocation around the archway or he knows that there is a maximise/empower fireball that gonna blow up if he step on that plate around the corner?

I did'nt found anything that adress that question neither in detect magic spell description nor in the trap section.

Thanx

Also depends on which side of the stone archway the trap is. If it is on the other side of the thick stone archway (just around the lintel, so to speak) then it would be shielded from detection by the stone in front of it. Detect spells do not go around corners. So a 1 foot thick stone lintel, for example, would stop the detection of a magic trap on the other side of it, aimed down. At least by detect magic. A good perception check will still point it out.


Adamantine Dragon wrote:

In the case of the magical fireball trap listed above, unless the trap is shielded, a moderate aura of evocation would be detected.

It would be a rare adventurer who did not immediately say "Crap! Fireball trap!"

They wouldn't "know" it was a fireball, much less an empowered one, but they'd know something was likely to go boom.

A Wand of Fireball also detects evocation. So does just about every magic weapon.

It would indeed be the rare adventurer who didn't closely investigate every magic aura they detect, which could very well set off the very trap they were investigating.


Pathfinder Starfinder Roleplaying Game Subscriber

I always assume that a good magic trap has Magic Aura used on it. Given that a magic trap has to have detection magic and the spell effect's magic school, adding a low level illusion shouldn't be too much of a stretch to what already has to be a magic mix.

So for me it comes down to the skill and mentality of the creator. If the trap was crafted right, it would be hidden in every way it needed to be done. If it was done hastily or by a less capable mage, or on the cheap, then let detect magic work. Ruins for magocracy societies might let magic traps be detected by the elite mages of the day, adding to their power and mystique, with hidden vault areas designed to stop rival mages suddenly hiding the aura.

I've had fun with a middle road, area traps that return as magic circle or illusion magic, something interesting to draw the party but not immediately thought of as harmful, or door traps that show as alarm or arcane lock spells.


Part of using Spellcraft to identify a magic item also involves examining the item. If someone wants to identify the magic aura coming from a trap, they are going to spring the trap because they will be attempting to closely inspect the trap!

Since they are looking at the trap as they approach it, you should give them a perception check to realize what they are about to touch looks like a trap! I would give no bonus or penalties on this check, being allowed to find a trap without stating you are looking for one is already getting something extra.

And magic traps aren't magic items. The correct skill for dealing with that would be disable device.


Since this is the Rules section, Detect Magic states only that you sense magical auras in a 60' cone-shaped emanation. Under the Magic rules it says that such cones begin at the caster and radiate forward, so either the caster IS detecting some of the auras of their allies' items/buffs if those allies are in the cone, or if the caster has moved to a point where their party is beside/behind them they don't detect these allies.

That being said, further information requires rounds. Round 1 is the presence or absence of magic, round 2 is number of auras and the relative power level of the strongest one, and round 3 is the strength and location of every aura detected. On round 3 you can try to ID the school of magic of the aura(s) detected. Since several folks have confirmed it yes; traps aren't magic items by RAW so you can't just identify them using Spellcraft.

The question comes down to what auras would emanate from a trap? By RAW, while the GM CAN say that the trap's triggering spell such as Alarm is concealed by 1' of stone, 1" of common metal, a "thin sheet" (no precise measurement) of lead or 3' of wood or dirt, obscured by Mystic Aura, or otherwise obfuscated in some way, this isn't automatic by RAW. What IS automatic, however, is that a spell to harm/impede others is concealed in a location, triggered by some kind of Trigger as defined by the Traps section.

Nothing in the Traps section suggests that spell meant to harm/impede a victim or victims is active and since this isn't a magic item this spell wouldn't radiate from the trap, so in the above instance the Fireball spell wouldn't really be detectable by RAW until it went off. While it's LIKE a spell completion item it isn't technically a magic item, so the Fireball doesn't register.

However under RAW there is nothing that automatically conceals the Trigger mechanism of a trap, other than the very nature of the trap. Looking at mechanical traps, their Trigger mechanisms aren't technically detected unless the Perception to detect the trap is rolled. In other words, the rules on Traps in that section assume that SOMETHING is being done to hide the mechanism that triggers a mechanical trap, so when you hit the Perception check to detect the trap what you're actually identifying is the trigger mechanism, unless you exceed the roll by 5 or more.

A spell trigger however is, by it's very nature, invisible so there's no assumption that anything is done automatically to obscure it further. The GM will have to make a decision on a trap-by-trap basis what, if anything, the trapmaker did to conceal the trigger spell from being detected.

Then there's the actual ACTION of Detect Magic. If this spell is constantly running from, say, a class ability or a magic item then it's just on and you can jump right to round 1 but if cast as a 0 level spell or used from a consumable item, the user likely has to speak a command word, uncork a bottle, or use verbal and somatic components and a Standard action to activate it. There's no action type defined in the spell's extra rounds of detection but it suggests there's concentration involved. Under the Magic section concentrating on a spell is Standard action as well so presumably the caster is spending three rounds of their Standard actions staring into the cone-shaped emanation of their spell, determining all of the information mentioned above.

I bring this up because 1. if the Fireball is triggered by Clairaudience (sound) and the PC cast their spell close enough the trap goes off, regardless of their detection, and 2 this would be a perfect time for some predatory monster to attack the caster whose Standard action is otherwise engaged.

So... if the Fireball trap in the OP is concealed by an archway, depending on exactly what the location of the trigger spell is a PC spellcaster COULD detect that spell trigger. The OP mentions stepping on a plate, so presumably the plate houses the trigger. If the plate is any of the concentrations of material I mention here Detect Magic fails. Otherwise round 1, a caster detects an aura ahead; round 2 they detect the spell trigger on the plate (unless their allies are confusing things) and round 3 they can make a Knowledge: Arcana check, DC 15 plus the spell level of the spell on the plate to identify the school of the spell trigger.

Or just have folks make Perception checks to find traps. Honestly, there's no distinction between magical and mechanical traps other than the fact that magical ones are tougher to find. Considering an optimized PC with a free Skill Focus feat could have roughly a +11 or better Perception check starting from level 1, just having a PC get close and make their Perception check does the same job of finding the trigger.


1) the lead required to hide the magical rune/sigil/whatever portion of the trap would be negligible. A few copper, and easily assumed to be part of the cost of the trap. Certainly not expensive enough to impact its CR

2) If a trap requires a perception check to detect, then it is hidden.

3) A trap is not hidden if you do not put the sigil/rune/whatever behind a few coppers worth of lead.

4) If RAW says a trap is hidden, then tjhe trap is hidden from detect magic. No houserule required.

Very rare exceptions could be made for magical traps that somehow occurred naturally and were not placed/made/hidden by a creature with any intelligence or intentions.


This is some popular necromancy.

It's a bit of an unexpected conflict created by having unlimited cantrips. In 3.5, cantrips use up slots just like regular spells. So, magic traps were designed assuming you couldn't just spam detect magic all day long.


Melkiador wrote:

This is some popular necromancy.

It's a bit of an unexpected conflict created by having unlimited cantrips. In 3.5, cantrips use up slots just like regular spells. So, magic traps were designed assuming you couldn't just spam detect magic all day long.

Very true and I agree, but I also agree with Pants Castle up there too; concealing the Trigger spell (Alarm, Clairaudience what have you) should be factored into the cost of the trap. Think about it; Detect Magic is foiled by 1" of "common metal"; let's say iron, or nickel, or tin, or brass, or whatever.

If the GM has been consistent enough in their descriptions of the environment that a 1'x 1' x 1" thick metal tile wouldn't be out of place, or the actual metal is in turn concealed beneath a thinner-than-normal flagstone in the floor, there's no way that a PC, using Detect Magic, would automatically notice the trap by RAW.

This would instead fall back on a Perception check first to detect the trigger mechanism of the trap or, if they beat the DC by 5 or more, detect the trigger and get other clues about what the trap might do.

Y'know, it just occurred to me while typing this: Alarm one of the lowest level spells suggested as a Trigger mechanism spell wards an area of a 20' radius and nothing in the spell says that it fails through, say, 1' of stone. If spell traps weren't so freaking expensive I could imagine whole dungeons warded with Alarm spells every 20' concealed inside the walls.


Alarm's detection radius is an emanation, and would be blocked by anything that would block its detection. You'd also detect the alarm effect at its edge, not its center. But you could use a mundane detection method hooked to a magical trap that was within a lead lunchbox.

It's probably simpler to abuse the multiple-magical-auras/local-magic method of confusing detect magic instead. There's no size limit on the size of symbols made for symbol spells, so it's not too complicated to slap one of those things on the whole region and always have a much more powerful spell detected. Symbol of scrying seems built for this purpose. And if your actively scrying, you can set things up to trigger some traps manually, ignoring the difficulty of concealing trigger mechanisms.

I also recommend using the "detect scrying" spell as a proximity trigger. In a world where people use detect magic as a way of searching for traps, you may as well have traps that are set off when people try to detect magic.


Something that happens in the RotRL AP is that Thassalonian construction includes a preserving magic in their construction. Not only does this help to explain how the construction survived 10,000 years of neglect, it also puts several magical auras over the entire dungeon. It doesn't make detect magic useless, but it does mean you need to filter out the background immediately if you want any useful information.

And filtering out that background would filer out the traps since you're trying to ignore the magic walls everywhere else.


I feel like putting a lead sheet over the trap's trigger ought to block the trigger from working. It would be like trying to conceal a security camera by encasing it in a metal box.

Shadow Lodge

Do you think detect magic allows you to see a person who is hiding, but wearing a magical ring? I am inclined to say you would need to make your perception check vs his stealth in order to see them or you wouldn't detect the magic. I'm sure there's people who would say the opposite though, either way, a trap should function the same.


gnoams wrote:
Do you think detect magic allows you to see a person who is hiding, but wearing a magical ring?

It wouldn't allow you to see the person, but you'd probably detect there was a magical aura in the area, unless they were hiding behind a sheet of lead or equivalent. (See Detect Magic versus Invisibility...)


Cheapy wrote:

And many more just run it as is.

After casting Detect Magic, they will detect there's magic around. They will detect where the magical trap is after 3 rounds of studying. Assuming it's a normal magical trap (triggered by alarm), they will detect that abjuration. The fireball has not happened yet, so I see no reason for them to detect the evocation. You could always be nice to let them try to identify the trap as you would an item, and learn what it does.

But I think RAW, you would just detect the abjuration, or whatever else the trigger is.

Literally the very first entry on the knowledge skill table

Quote:
Identify auras while using detect magic | Arcana | 15 + spell level


Pathfinder Adventure Path, Rulebook Subscriber

Just remember: Explosive Runes is an Abjuration spell. ;)

And if there are runes carved into the doorframe and the player detects it as magical, their Spellcraft would go "Abjuration magic runes" after three rounds of focus. Make the runes small enough that you get within 5 feet and when they try to decipher the runes?

Boom.

The second door will also have Abjuration magic runes. It holds a demon trapped behind it, so Dispel Magic or Erase means the demon gets loose and gets to try and kill the party... ;)

Liberty's Edge

Pathfinder Companion Subscriber; Pathfinder Roleplaying Game Superscriber
gnoams wrote:
Do you think detect magic allows you to see a person who is hiding, but wearing a magical ring? I am inclined to say you would need to make your perception check vs his stealth in order to see them or you wouldn't detect the magic. I'm sure there's people who would say the opposite though, either way, a trap should function the same.

Hiding requires concealment. So to hide from Detect magic you need concealment against that. It can be a sufficient quantity of material or a different magical aura. It does not need to cover the hiding person completely but it should be enough to make the detection difficult. So hiding behind a box or statue works while a shadowed area isn't enough.

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