How are traps found?


Rules Questions


So, say a trap is located in the center of a 50 by 50 foot room. The range of vision the trap has is 40 ft. How exactly can a character discover the trap before it springs if the trap is located in the center of the room? They'll spring it before they can get near the spot to search.

Or does the area where the trap affects also count as the entirety of the trap? As in, searching an area where a trap will affect if sprung is the same as searching for the source of the trap?

Dark Archive

Usually a trap has a point of origin for its effect and one or more triggers.
Let's say a swinging pendulum with an axe blade affixed to the ceiling and hidden in painted cracks along the stonework (point of origin) triggered by a large pressure plate or transucent tripwires (trigger points).

A magical trap that has an area of effect greater than the distance between its point of origin and the trigger point (the range of vision, I suppose), is quite clever in theory books but bound to frustrate players to no end, as they have virtually no means - excluding clever divination magic or clues dropped previously - to discover and avoid it.

Sounds like a bad design.


Razz wrote:

So, say a trap is located in the center of a 50 by 50 foot room. The range of vision the trap has is 40 ft. How exactly can a character discover the trap before it springs if the trap is located in the center of the room? They'll spring it before they can get near the spot to search.

Or does the area where the trap affects also count as the entirety of the trap? As in, searching an area where a trap will affect if sprung is the same as searching for the source of the trap?

By RAW someone searching for traps can just take a -1 for each 10 ft of distance between the searcher and the trap.

The Exchange

The standard response here has to be 'send a hobbit into the room to see if anything goes boom...' but I'm guessing that's not too helpful... ;)

Traps have a Perception DC to spot them, so the normal Perception penalties apply. If the Perception DC to spot the trap is 20, then you can spot it 50ft away with a Perception Skill roll of 25 (assuming no other modifiers).

Personally I often find it easier, as a DM, to work backwards from the rolled Perception check to the range the character notices the thing percieved at. I.e. as DM I'd make a secret roll for the PC's Perception check to notice the trap, then compare it to the Perception DC of the trap and count the range the trap is noticed at as 10ft per 1 over the required Perception DC which was rolled.

E.g. the trap has a Perception DC to be noticed of 20. The party Rogue is scouting ahead, and approaching the trapped room. I secretly roll to see if the Rogue notices the trap and score a 27. The Rogue spots the trap 70ft away.

A trap's own 'range of vision' is usually limited in at least the same manner as a character's - so traps usually can't 'see through doors' in the case of, for example, your 40ft range of vision trap being in the centre of a 50 x 50ft room behind closed doors. But that gives the potential problem of a trap 'auto detonating' when the door's opened. The generic Perception rules work here as well - through a closed door is, for example, a +5 DC to notice the trap. If the character does notice it then perhaps he heard some tell-tale mechanical whir or click as the trap cycled, or smelled a distinct tang of ozone in the air he recognises as indicative of some type of magical trap... however you choose to describe such things, the Perception rules basically cover it. This is why Rogues need that bonus to Perception checks to spot traps in the first place... it's not always easy! ;)


ProfPotts wrote:
A trap's own 'range of vision' is usually limited in at least the same manner as a character's - so traps usually can't 'see through doors' in the case of, for example, your 40ft range of vision trap being in the centre of a 50 x 50ft room behind closed doors. But that gives the potential problem of a trap 'auto detonating' when the door's opened. The generic Perception rules work here as well - through a closed door is, for example, a +5 DC to notice the trap. If the character does notice it then perhaps he heard some tell-tale mechanical whir or click as the trap cycled, or smelled a distinct tang of ozone in the air he recognises as indicative of some type of magical trap... however you choose to describe such things, the Perception rules basically cover it. This is why Rogues need that bonus to Perception checks to spot traps in the first place... it's not always easy! ;)

Keep in mind, too, that it's very rare to find a trap that doesn't have some means of legitimate people bypassing it. What good is putting the perfect trap on your treasure room, if it keeps you out as well? Any trap that gets activated because it can see you as soon as the door got opened is a poorly designed trap.

Admittedly, there's apparent exceptions - a lich might happily put negative energy based traps all throughout his lair, with no method to bypass them, since they don't affect him or his undead minions. In this case, the method to bypass the trap is to be immune to negative energy.

While that's usually more an argument for Disable Device, it's applicable to perception when the trap is set up so that it would auto-detonate.


For a lich those negative energy traps are more than just a trap -- they are a source of free magical healing too, which makes them doubly useful.

However to the OP's question: You make a perception check. If you are searching for traps (and you beat the perception DC) you should find it before it can go off.

Anything else isn't a trap -- it's simply GM fiat to hurt the PC.

Dark Archive

Abraham spalding wrote:

For a lich those negative energy traps are more than just a trap -- they are a source of free magical healing too, which makes them doubly useful.

However to the OP's question: You make a perception check. If you are searching for traps (and you beat the perception DC) you should find it before it can go off.

Anything else isn't a trap -- it's simply GM fiat to hurt the PC.

Reminds me of the old Dragon magazine "Wandering Damage Table"

Spoiler:

How To Use The Wandering Damage System

First there was the wandering monster. They serve well when applied in hordes, but why not cut out the middleman and just deal out damage to the characters directly? It makes for a smoother, faster-paced game, and if you want to kill off characters quickly, it can only be beaten by divine intervention by Cthulhoid godlings.

Instructions: Whenever a player annoys you in any way, by wearing tasteless clothes or eating the last corn chip, ask him to roll a d20. He may become worried that he's rolling a saving throw. Ha, ha!!! Little does he know that he just rolled on the Wandering Damage System matrix!!! Repeat the roll as often as desired.

The Wandering Damage System Matrix

Roll Result
1 Your character has fallen down a flight of stairs; roll his dexterity or less on percentile dice, or else consult Limb Loss Subtable.
2 The monster your character just killed gets up and attacks him, doing 8-80 points of damage.
3 Your character smells smoke; his right arm is on fire. Take 14 points of damage and save vs. gangrene.
4 Your character cuts himself while shaving; consult Limb Loss Subtable.
5 Your character's nose hairs catch fire and he dies of smoke inhalation.
6 Your character stumbles backward into a yawning chasm and disappears from view.
7 The next time your character says something, he eats his words, chokes on them, and dies.
8 Something cuts your character's nose off, doing 2-12 points damage and really messing up his charisma.
9 Your character steps on a piece of glass; consult Limb Loss Subtable.
10 Your character suddenly catches a severe case of brain death.
11 Something invisible chews on your character, doing 6-36 points damage.
12 Your character develops an incredibly severe case of arthritis and can grasp nothing with his hands; he drops anything he's holding - and if that happened to be a sword or an axe, consult the Limb Loss Subtable.
13-20 Consult the Random Damage Subtable for no reason whatsoever.

Limb Loss Subtable (roll d6)

1 - Left leg gone
2 - Right leg gone
3 - Left arm gone
4 - Right arm gone
5 - Head gone
6 - Torso cut in half

Random Damage Subtable

Dice roll Result
01-05 Take 10 hit points damage.
06-10 Take 15 hit points damage.
11-20 Take 30 hit points damage.
21-25 Take 10 hit points damage and consult Limb Loss Subtable, modifying die roll by +5.
26-30 Take 10 hit points damage and roll again on Wandering Damage System Matrix.
31-35 Take 15 hit points damage and then take 30 more.
36-40 Roll every die you own for damage.
41-45 Take 17 hit points damage.
46-50 Take 42 hit points damage.
51-55 Multiply your character's age by 5. Take three times that much damage.
56-60 Take 24 hit points damage and then take 31 more.
61-65 Take 1,000 hit points damage and roll again.
66-70 Roll every die within 30 feet for damage.
71-73 Add up the total hit points of everyone in the party. Take that much damage.
74-75 Take 3 hit points damage and consider yourself very lucky - for the time being.
76-00 What? You didn't get hurt? That's impossible - this system is foolproof. Roll again.

(Wandering Damage System is copyright TSR April 1985 and reproduced here as a small extract from an entire magazine for purposes of review and parody.)

Dark Archive

ProfPotts wrote:
all sorts of interesting stuff

very insightful ProfPotts, thanks. That's just what I needed to explain trapfinding in the story :)


Depends on the trap really - some conceal it better than others.

RPG Superstar 2008 Top 32

I removed an offensive post.

Liberty's Edge

...and now I'm left wondering how anyone could have possibly thought of anything offensive to say in this thread.

*scratches head*

The Exchange

Yeah, how could someone fall into that trap?


Jeremiziah wrote:

...and now I'm left wondering how anyone could have possibly thought of anything offensive to say in this thread.

*scratches head*

Me too.


Jeremiziah wrote:

...and now I'm left wondering how anyone could have possibly thought of anything offensive to say in this thread.

*scratches head*

Some people are just good like that, I guess.


Pathfinder Companion, Starfinder Adventure Path Subscriber; Pathfinder Roleplaying Game Superscriber

I have a question that is related -

Glyph of Warding

How does someone with trapfinding disarm this? I figure someone with 'Use Magic Device' can manipulate it so that it doesn't go off, and it can be dispelled - but how do you disable it?

(Yes, I know technically, all you have to do is roll 'disable device' but I just don't get the how it works)

Dark Archive

chavamana wrote:

I have a question that is related -

Glyph of Warding

How does someone with trapfinding disarm this? I figure someone with 'Use Magic Device' can manipulate it so that it doesn't go off, and it can be dispelled - but how do you disable it?

(Yes, I know technically, all you have to do is roll 'disable device' but I just don't get the how it works)

Maybe the scratch off some important part of the rune (if it is not touch activated), or flick paint at it to foul up some special part of it if it is touch activated. I have heard it described many ways. One DM described it as the character using a small steel rod to "ground" out the spell in the rune, or fanning heat from a torch at a touch triggered one to remelt the mercury/phosphorous paste that was part of the rune, causing it to run down and break.

The Exchange

I have always ruled that the trap DC is based on its area of effect - not its point of origin.

If a trap has a 30 foot radius, you can interact with it at the edge of its effect. Even for a magical trap. An un-disarm-able trap is outside of the RAW as far as I understand, and such would be a plot device. There is no getting around those damn things.

Rogues notice stuff - it's the GM's job to describe how. Maybe the hairs on the back of their neck stand on end, or maybe there is a haze in the air that they perceive. Make it up.

As for disarming, that too is up to the GM. Some GM's just say "meh, it's disarmed." Others will describe how using a handful of old dust sprayed through the air baffles its sensitivity to passing creatures long enough for the party to slip by. Or maybe the trigger isn't actually everywhere, and the rogue can feel around based on the tension in the air and avoid those spots and the party can slip by.

In the case of them disarming it completely, maybe they confuse it until they get close enough and then do something else.

Make it up.


Pathfinder Companion, Starfinder Adventure Path Subscriber; Pathfinder Roleplaying Game Superscriber

How about taking a example from one of Paizo's APs.

There is a greater glyph of warding placed on several doors. All of the glyph have magic aura cast on them to make the doors non-magical (I am assuming that this raises the search DC, but honestly am not sure).

The glyph is on the inside of the door and it triggered when someone who does not fit the criteria (in this case worship of a specific demon) passes through the door - at which point the glyph has a burst radius of 5-ft.

If the PCs are on the outside of the door...


chavamana wrote:

How about taking a example from one of Paizo's APs.

There is a greater glyph of warding placed on several doors. All of the glyph have magic aura cast on them to make the doors non-magical (I am assuming that this raises the search DC, but honestly am not sure).

The glyph is on the inside of the door and it triggered when someone who does not fit the criteria (in this case worship of a specific demon) passes through the door - at which point the glyph has a burst radius of 5-ft.

If the PCs are on the outside of the door...

Then the designer didn't really pay any attention in trap design school (in my opinion -- don't get me wrong paizo does some amazing stuff -- but their APs always come off lacking in my opinion -- too many rules missed, encounter designs mangled -- the stories generally are great, the arch usually inspired, and the basic premises of encounters good... it's the execution that lacks).

5 foot blast isn't going to travel through the door (by the way the non-magical aura is pretty much useless against rogues who don't use magic to find traps), and since it's a burst instead of a spread it isn't going to go around the door at all (imo).

Scarab Sages

R. Doyle wrote:
An un-disarm-able trap is outside of the RAW as far as I understand, and such would be a plot device.

Eh, yes and no. By adding 3 to the trap cr, you can set the disable device dc at any number 30 and higher. Meaning you can set the dc at ten million to disable the trap for a simple +3 to the cr.

The Exchange

Magicdealer wrote:
R. Doyle wrote:
An un-disarm-able trap is outside of the RAW as far as I understand, and such would be a plot device.
Eh, yes and no. By adding 3 to the trap cr, you can set the disable device dc at any number 30 and higher. Meaning you can set the dc at ten million to disable the trap for a simple +3 to the cr.

That falls into the "plot device" area for me, but I see how RAW it is possible...

Dumb. But possible.


Disarming traps on the other side of a door require tools (duh). For example, a mirror on a steel rod (think the little mirror the dentist uses).

Of course, this can be a bad thing too (symbols go off when you see them).

But in general, disarming the glyph on the other side of the door is just a case of finding it (using the mirror on a stick), and then using other tools that allow you to slip things under a door to, say, squirt some ink up and on the glyph thus altering it.

Dark Archive

mdt wrote:

Disarming traps on the other side of a door require tools (duh). For example, a mirror on a steel rod (think the little mirror the dentist uses).

Of course, this can be a bad thing too (symbols go off when you see them).

But in general, disarming the glyph on the other side of the door is just a case of finding it (using the mirror on a stick), and then using other tools that allow you to slip things under a door to, say, squirt some ink up and on the glyph thus altering it.

I think that viewing the symbol via a mirror should fall under the gaze attack rules. That viewing it via a reflection does not set it off (or reduces the chance if nothing else).

The Exchange

The fluff of finding and disarming traps is left deliberately vague, just like most other descriptive stuff in the game, so it's basically down to what the DM wants to describe.

Some suggestions would be...

Finding:

Senses other than sight - e.g. hearing a strange hum, a slight whir and click, or a footstep ringing a little more hollow than usual; catching the scent of ozone or grease; feeling a slight shift in temperature or air pressure; simply feeling the hairs on the back of one's neck rising.

Evidence of previous victims - anyone who's watched any modern police forensic drama knows the bad guy can never clear away all the evidence... Maybe a scorched spot on the floor, a splatter of dried blood, some fragments of powdered bone... any or all in a pattern which indicate (to the trained eye) some sort of trap.

Disarming:

'Mechnaical' disarming is easier to get your head around (jam up the works, snip a vital piece of rope, knock out a pin here or there), but disarming magical traps can be even easier to describe - just fluff it that the Rogue has picked up some minor magical talents which disarm magical traps - a chant and a gesture and it's done. The main issue with the 'mar the symbol with ink' way of doing it (although it's a completely reasonable way to describe such things) is the possiblity of some bright spark then using 'logic' and just chucking a load of paint (or whatever) into potentially trapped rooms... This will vary a lot based on how much your players tend to 'try it on', of course... ;)


Happler wrote:
mdt wrote:

Disarming traps on the other side of a door require tools (duh). For example, a mirror on a steel rod (think the little mirror the dentist uses).

Of course, this can be a bad thing too (symbols go off when you see them).

But in general, disarming the glyph on the other side of the door is just a case of finding it (using the mirror on a stick), and then using other tools that allow you to slip things under a door to, say, squirt some ink up and on the glyph thus altering it.

I think that viewing the symbol via a mirror should fall under the gaze attack rules. That viewing it via a reflection does not set it off (or reduces the chance if nothing else).

Decent house rule. Maybe add to the save bonus or something.

Liberty's Edge

chavamana wrote:

How about taking a example from one of Paizo's APs.

There is a greater glyph of warding placed on several doors. All of the glyph have magic aura cast on them to make the doors non-magical (I am assuming that this raises the search DC, but honestly am not sure).

The glyph is on the inside of the door and it triggered when someone who does not fit the criteria (in this case worship of a specific demon) passes through the door - at which point the glyph has a burst radius of 5-ft.

If the PCs are on the outside of the door...

As a minimum you get the +5 DC for "perceiving" it through a closed door.

Setting it on the actual door surface, as already said, don't work. It should be set on the side (what side depend on the direction in wick the door swing) so that it will hit the guy opening it.

Something like this with the * being the glyph.
_/*_

A canny rogue noticing it can "disarm" it opening the door with a rod wile keeping total cover.

Happler wrote:
mdt wrote:

Disarming traps on the other side of a door require tools (duh). For example, a mirror on a steel rod (think the little mirror the dentist uses).

Of course, this can be a bad thing too (symbols go off when you see them).

But in general, disarming the glyph on the other side of the door is just a case of finding it (using the mirror on a stick), and then using other tools that allow you to slip things under a door to, say, squirt some ink up and on the glyph thus altering it.

I think that viewing the symbol via a mirror should fall under the gaze attack rules. That viewing it via a reflection does not set it off (or reduces the chance if nothing else).

Viewing the symbol is one of the ways to activate it, but viewing it is not a requirement for it affecting you. It require a line of effect but, for example, closing your eyes do nothing against its effects.

The symbol radiate the effect like a burst, so if the door is between you and the symbol you are protected by the door.

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