Being a set of tables for generating concepts for traps for any system, with examples and discussion.

Tables

Purpose of Trap (d8)

1. Capture
2. Impede
3. Injure/Kill
4. Resource Sink
5. Hazard
6. Practical Joke
7. Lock/Barrier
8. Alarm

Trigger Type (d12)

1. Pressure Plate
2. Trip-wire
3. Opening a container/door
4. Removing pressure
5. Occlusion
6. Heat/Light
7. Magnetism
8. Guard-activated
9. Permanent
10. Sound
11. Unusual Sense
12. Timed

Location (roll separately for trigger and trap, d6)

1. Floor
2. Wall
3. Ceiling
4. Container
5. Entrance
6. Other

Obviously, some effort needs to be spent to make the trap coherent; if the trigger is a pressure-plate on the ceiling for a trap on the floor, it should be something like a place the door will brush as it’s opening, or be part of a feature on the ceiling like a mosaic or chandelier that the players will be tempted to explore.

Mechanism (d10)

1. Gravity (pit trap, falling block, tilting floor, sharpened pendulum)
2. Spring-loaded (arrow or spear)
3. Clockwork (crushing walls, retracting catwalk, portcullis releasing beast)
4. Hydraulic (liquid filling area, rising floor)
5. Chemical (gunpowder, chemicals combining to form noxious fumes, acid)
6. Physical Properties (flammable material, radioactive, poisonous)
7. Magical (known magical effects and spells, such as magic mouth, or fireball)
8. Electronic (electrifying areas, as well as hi-tech substitutes for clockwork)
9. Biological (spores, parasites, released critters)
10. Arbitrary (magic not using known/documented spells)

Notes

Purpose of Trap

Capture

A Capture trap attempts to hold victims until they can be dealt with later; in some cases the trap is meant to hold them until they expire from natural causes or injuries suffered.

A pit trap is the classic capture trap, though others might throw a net or sticky substance, or simply lock adventurers in a room with no way out.

Impede

Impedance traps are meant to slow down victims, either to make them easier to catch or increase the likelihood of patrols running into them.

Classic impedance traps include mazes, caltrops, sticky or slippery floors, magically darkened areas, or cryptic messages that adventurer’s may waste time trying to decipher.

Injure/Kill

Injury traps are intended to harm the victim, perhaps killing them outright.

Classic injury traps are pit traps (if deep enough or with spikes), spear or arrow traps, swinging blades, falling blocks, crushing walls, poison darts, and the like. Some can be dodged or defended against (particularly ones that poke or slice with a regular weapon), or depending on damage rolled might not injure you that much. Others, such as being dumped into lava or having cockatrice feathers poured down over you, are meant to be lethal so they have to be avoided, whether through noticing the trigger or making a saving throw.

Resource Sink

Traps that cost resources are meant to deplete the intruder’s stock of available resources, softening them up for later, or perhaps stranding them if they turn out not to be carrying enough torches or rope to get through the area.

Resource traps might be stretches that require a lot of technical climbing (with spikes and ropes, or use of fly spells), or passage through long underwater sections, or strong magnets that make the party abandon iron gear (a rust monster is the animate version of this), or contain things like slimes or oozes that eat away at wooden or leather gear.

Hazard

Some “traps” aren’t designed as such at all (or at least not designed by any creatures in the gameworld), but are simply hazardous areas. Narrow mountain passes prone to avalanches, or areas with volcanic fumaroles, or treacherous ice don’t have a specific design goal, they are simply there and dangerous if you try to traverse them.

Practical Joke

Some traps are designed to amuse the placer of the trap, and often do no more than inconvenience or embarrass the victim. These may also serve as alarms or to discourage intrusion in places where it would be unwise to put a trap that can actually injure or kill. E.g. a wealthy merchant probably won’t have a pit-trap with poison spikes in his town-home to keep his servants out of the liquor, but might put lampblack on the knobs of the cabinet to stain their hands.

The real-world version is a bucket over the door or a whoopee cushion. Magical traps of this sort planted by a whimsical wizard or fairy might curse somebody with an animal’s head, or change their sex.

Lock/Barrier

Some “Traps” are just meant to prevent access to unauthorized people. The simplest is just a locked door or gate. Elaborate or magical ones may involve puzzles, perhaps an entire room that forms a puzzle. There might be consequences, including lethal ones, for making a wrong move in the puzzle, the essence is to actually to provide a means of ingress to somebody who knows the secret, not to keep everybody out permanently (as might a rolling boulder or falling block trap in a tomb).
Note that some locks or barriers aren’t there to prevent adventurers from getting in, but to keep something dangerous from getting out….

Alarm

Alarms aren’t intended to directly harm those triggering them, but to alert others to the fact they’ve been triggered.  They might respond by arranging an ambush, or by running away with the treasure.

Trigger Type

Pressure Plate

A Pressure Plate is any sort of pressure sensitive mechanical trigger. It is usually activated by stepping on it, and typically has some threshold weight that is too small to trigger it (whether that’s a coin, a mouse, or a hobbit).

It can typically be detected by careful examination of the area for a mismatch in the height of the material, seams where the plate meets the rest of the area, a slight wobbliness or give if manipulated; because of the presence of a mechanism beneath the plate, sand or water may be able to flow through the seams where it wouldn’t in ordinary crevices.

Pressure plates can often be jammed by wedges in the seams or levered beneath the plate, or can by bypassed by not stepping on them.

High tech or magical pressure plates may be nearly impossible to detect, save by detecting the presence of magic or electricity itself, though a fair trap will still usually a least be triggerable by dropping a sufficient weight on it.

Trip-wire

Trip-wires are any sort of physical wire, rope, or cord that triggers a trap by pulling on something when somebody steps on or through it.

They can often be spotted by visual inspection, though if they are camouflaged, very fine or in bad lighting conditions they can be extremely hard to spot without unusual senses; adventurers of unusual size (small enough to pass beneath) or means of locomotion (always flying) may bypass them without even noticing.  They may also be detected, or at least triggered, by poking ahead with a pole.

They can be bypassed by stepping over or under them, or jammed by preventing the wire from moving or breaking.

Opening a container/door

Opening a container or door can trigger a trap by the mechanical action of the hinges, by the lid or door pushing or pulling something as it changes position, or releasing pressure on a spring, by the twisting or pulling of a knob or handle attached to the catch that holds it closed, by poison on the handle or on something sharp that someone manipulating the handle is likely to cut himself on  or simply because the container or room has something dangerous in it.

Spotting such traps can be difficult unless you have unusual senses allowing you to see inside the container, since all the mechanical parts of the trap may be on the inside.  It might be possible to detect the trap by an slightly higher resistance to opening than expected (particularly if the hinges are well-oiled first) or the sound/feel of something scraping or being pulled.

Such traps can be bypassed by creating a new opening in the container, by breaking a wire or flange that would be pulled out of position by opening the lid, by applying pressure to a spring that would otherwise release, by manipulating the knob or handle remotely or through protective gear.

Removing pressure

Pressure triggers can be set off when something is removed from where it should be, such as when a heavy gold idol is taken off an altar, allowing a spring to uncoil, the other end of a counter-weighted lever to descend, or weight that was held in place by a cord beneath the idol to fall…

Spotting such triggers can sometimes be done by seeing the cord or noticing the seams where the trigger mechanism will move once the weight is gone.

Disarming the trap can be done by swapping the weight for a similar one (be careful that the replacement weight is close enough… particularly if the builders took extra care so that if too much extra pressure was applied to the balance the trap would trigger anyway), or by jamming the balance platform so that it can’t move even if the pressure is removed.

Occlusion

Occlusion triggers are set off when something blocks the sensor, as with an “electric eye.”  These usually require magic or high technology, though a goblin with a peephole would do in a pinch.

They can be spotted by noticing the opening for the sensor, or if the sensor requires a visible beam of light (or one that can be made visible, say with smoke) the beam.

They can be bypassed by avoiding breaking the beam or passing in front of the sensor, or by arranging mirrors to divert the light in a path that reaches the sensor but leaves space to pass.

Heat/Light

Heat/Light triggers are set off by the presence of extra heat or light, such as generated by torches or just by warm-blooded creatures.  The trigger might be an exotic material that melts easily, releasing a spring or a weighted cord, or perhaps the material itself is poisonous once it’s heated enough to form a vapor, or perhaps phototropic plant that pulls or pushes the trigger as it turns toward the light.  Or it could just be magic or tech.

Spotting such traps will be very difficult without some way to observe the trapped area remotely or in perfect darkness.

Bypassing the trap might involve nothing more than being able to pass through the area in darkness, or by interfering with whatever mechanical part is connected to the sensor.

Magnetism

Magnetic triggers will usually have some catch that is pulled out of place by magnetic attraction, generally to the armor to the adventurers wear… though if the magnet is powerful enough it might itself be the trap, pulling the adventurers off a ledge or just immobilizing them unless they abandon their armor.

If it’s not obvious, a magnetic trigger might be detected by its effect on compasses, or by the very subtle pressure it exerts (a realistic magnet would have to be quite powerful if the metal isn’t going to come within a few inches of it, unless it was suspended in something to reduce friction. Otherwise the trap might as well be magical for all the adventurers can do to detect it).

Magnetic triggers can usually be bypassed by being careful not to bring metal near them, or by the usual mechanical jamming methods depending on what they’re attached to.

Guard-activated

Some traps are simply activated manually by a guard from an observation post.

Spotting the trap usually means spotting the guard, or at least the peephole or camera (or magical equivalent) the guard is using to observe the area.

Such traps can be bypassed by avoiding the field of vision of the guard, presenting the guard with a fake or illusory view of the area, taking out the guard, distracting or tricking the guard, or waiting for the guard’s attention to lapse (e.g. fall asleep, or leave the observation post to make rounds or relieve himself).

Permanent

Permanent traps don’t have a trigger, the area is simply dangerous (or dangerous to unprotected/unprepared people) all the time.  A room might be full of poison gas, so the only safe way to enter it would be if you were immune to the poison, took an antidote, or wore protective gear.

Depending on the nature of the danger it might be obvious to any observer, or it might only be revealed if you see somebody aware of the danger taking precautions.

Bypassing the trap usually requires ascertaining what precautions are necessary and taking them, since by definition there’s no way to avoid the trigger.

Sound

Sound triggers are set off by sounds or vibrations; they might be carefully balanced stones or snow (as in an avalanche), or a cavern or other structure that amplifies sound until it’s sufficient to dislodge a lever or weight.

Sound traps might be spotted by the area being unusually quiet or having peculiar echoes, or by observation of whatever pile of rocks or lever/pulley structure that’s the mechanical part of the trap before you get close enough for the sound to dislodge it.

Bypassing the trap could be done by being unusually quiet, by somehow stabilizing the delicately balanced trigger, or by jamming the mechanics if there is an accessible mechanical part of the trap and not just tons of stone that will fall from the ceiling if disturbed by loud sounds.

Unusual Sense

When magic or high tech is involved, many bizarre or nearly arbitrary phenomena might serve as a trigger.  (e.g. the presence of “good alignment”)  These usually can’t be spotted or bypassed unless you have appropriate magic or tech of your own, though you might still be able to infer the presence of the trap by observing the behavior of those “in the know” about it.

Timed

No actual trigger, rather the trap activates periodically, regardless of what’s going on.  A simple example would be a cavern that filled with water at high tide, but more complex ones might be something like pendulums that constantly swing, or walls that crash inward every few minutes.

Detecting timed traps can be done by noticing the remains of previous victims of the traps (since such traps are often unattended and automatically reset, so nobody ever takes the bodies away) or by observing the trap going off (since it will activate whether or not there’s reason to do so).

Bypassing the trap usually consists of figuring out the timing of the activation and passing through the area during the quiescent period.

Complications

Nastier traps often involve traps with precautions, fail-safe mechanisms, extra concealment or misdirection.

Precautions

Extra care might be taken to build the mechanism in such a way that it’s hard to interfere with.  For instance a trap where opening the lid of a box pulls a cord that activates a poison blade on a spring might make the cord out of wire so that it’s hard to cut even if spotted, or include extra metal baffles that extend downward from the lid so that you can’t poke a knife in until the lid is lifted enough for the cord to do its work.

Failsafes

Traps may have extra mechanisms to thwart attempts to disarm them; this can be an entirely separate trap that guards the mechanism of the original trap, or just extra precautions so that obvious ways of trying to disarm the trap trigger it anyway. For instance, using the example of a box and cord again, the trap could have an additional spring mechanism that puts tension on the cord so that if it’s cut the spring contracts and releases the poison blade regardless.  Or a trap that is triggered by a balance arm might be rigged so that it goes off if the balance goes in either direction (the idol is removed from the altar or the idol is replaced by something heavier).

Extra Concealment

Any trap can be made more dangerous by spending extra effort on concealing its mechanism.  This can range from the completely simple (painting the tripwire black, removing the debris from when the trap was activated previously) to the cunning (trompe l’oeil painting to deceive the eye as to the actual dimensions of the room or make the exposed parts of the trap completely blend in) to making the trap magically undetectable to all intents and purposes (illusions and invisibility fall into this category unless the characters have magic to deploy against it).

Misdirection

Some traps are concealed by the presence of obvious other traps or suspicious things.  E.g. an obvious pit-trap with an illusory floor trap just beyond it so that if the characters vault the first they land right in the second.  These are usually more amusing for the GM to contemplate than for the players to encounter, unless they are explicitly attempting to beat a “deathtrap” dungeon and are prepared to spend hours trying to out-paranoid a mad wizard with arbitrary resources in order to cross a 30’ corridor.

Still, in the real world there are such things as fake safes and dummy security cameras, so a certain amount of misdirection is probably allowable without being a complete bastard.