Developing my thoughts in
post 22 and
post 43, I think a good approach to traps would begin with a thorough treatment of triggers explaining how Perception/Investigation checks work with that trigger, what thieves' tools can be used for with that trigger, etc.
[SECTION]Why is describing triggers in more detail important? Think of my approach like the introduction to the Monster Manual. There's a section on "What is a Monster?", "Where Do Monsters Dwell?", explanation of monster types, explanation of a stat block. The UA article is kinda moving in that direction, but needs to go further. A trigger is the primary mechanism by which a character first interacts with a trap, and there really aren't that many triggers presented between the DMG and UA article, just 6 actually. Establishing a common mechanic/approach to each trigger (the same way 5e tries to do with similar spells) would go along way toward clearing up confusion about how traps work.[/SECTION]
Here's my take on the 6 common trap triggers that appear in the UA article and DMG (though I think there should be more)...
False Floors
Levers
Magical Wards
Pressure Plates
Spring Mechanisms
Tripwires
Trigger Types
False Floor
A false floor is a brittle or fragile section of floor, typically designed to conceal some variety of pit trap. It gives way when a certain amount of weight is placed on it (usually ~50 lbs).
Trap Examples: pit trap, spiked pit trap, gelatinous cub pit trap, acid pit trap, etc.
Notice: Most of the time, a false floor is undetectable. Wisdom (Perception) checks can detect signs of weathering where monsters skirt the false floor or periodically replace it, but will not identify the false floor itself. The exception to this is that a dwarf will automatically recognize the change in stonework used for a false floor built into stone.
Saving Throw: When a character triggers a false floor, they must make a DC 15 Dexterity saving throw as it crumbles away beneath them. On a failed save, the character falls into whatever trap awaits below the floor. On a successful save, the character can use a Reaction to grip the edge of what is now a hole, though this requires two free hands (i.e. dropping anything they were holding, which falls down the hole).
Disarm: Interpretting the signs of a false floor and skirting around it is the best defense, as is flying or levitating. Alternately, a false floor can be triggered with a sufficiently heavy object or a long plank can be laid across it allowing safe passage.
Encounter Design: False floors can be dangerous when used with particularly threatening pit trap, but their real danger comes from their ability to split the party. Additionally the threat posed by a false floor is magnified when encountered with monsters that Shove or otherwise inflict forced movement (e.g. minotaurs) or spells and effects that inflict forced movement (e.g. gust of wind). False floors are a great way to use a trap to tell a story, opening up a heretofor unexplored area of a dungeon.
Lever
A lever is a trigger that is deliberately pulled by monsters (or unwitting characters) to activate a trap. This includes winches, pulley systems, or any other mechanism that requires an action be taken to activate.
Trap Examples: falling gate, false doorknob, scything blades
Notice: Generally, a lever’s presence will be obvious, requiring no check to notice. However, sometimes a lever will be placed in a recessed alcove that is designed so it’s not visible until either in bright light or within 30 feet of a character with darkvision. Other times a lever will be disguised as something else, such as a doorknob, rung of a ladder, or even a book on a shelf.
Disarm: A lever can be switched off as an action. It can also be jammed with a piece of equipment such as a crowbar or dagger preventing it from being pulled. While thieves’ tools aren’t much help with disarming a lever, they can be used – given at least 5 minutes – to swap the on and off positions of the lever.
Encounter Design: A lever is usually placed in a place that’s hard for character to reach, but easy for monsters. Getting within 30 feet of the lever (mage hand range) should usually be a challenge. Sometimes, however, a disguised lever will be placed in plain view.
Magical Ward
A magical ward, like the glyph of warding spell, is a form of abjuration which triggers according to specifications defined by the spellcaster.
Trap Examples: any use of glyph of warding, fire-breathing statues, sphere of annihilation
Notice: A magical ward is almost invisible to the senses, though an Intelligence (Arcana or Investigation) check made as part of a thorough search – typically requiring at least 5 minutes – will discover barely perceptible glowing runes. If this check is made in pitch darkness it has advantage. Detect magic will always detect a magical ward as abjuration magic.
Disarm: Dispel magic cast at the appropriate level will disarm the magical ward. Depending on the individual ward, other means of disarming may be possible, such as dealing cold damage to a ward triggering a spell dealing fire damage. Thieves’ tools can’t disarm a magical ward.
Encounter Design: When used in moderation, magical wards can go a long way toward evoking a dungeon’s theme. It’s worthwhile to think of unique ways that characters can become aware of the trigger without detect magic and overcome it without resorting to dispel magic. If there’s a password or object to bypass the ward, consider which creatures in the dungeon know the password or possess such an object.
Pressure Plate
A pressure plate is a section of floor masked to look indistinguishable from the rest of the floor, that when a certain amount of weight is placed onto it (often about 50 pounds), and then removed from it, triggers a trap.
Trap Examples: falling gate, poison darts, rolling sphere
Notice: A well-designed pressure plate is usually not noticed until it is triggered, when a character feels it drop about an inch beneath them with a soft “click” sound. Causing structural damage, however, such as a thunderwave spell or a ring of blasting, will cause a pressure plate to vibrate. Additionally, a character with tremorsense can detect the presence of a pressure plate with a DC 20 Wisdom (Perception) check, due to subtle fluctuations of the plate in response to creatures moving across the floor.
Disarm: The easiest way to handle a pressure plate is to find a suitably heavy object to weigh it down, thereby freeing a creature to step off of the plate safely. However, tearing out nearby flagstones – requiring at least 5 minutes – allows a character using thieves’ tools (or ball bearings) to prop up the plate so that it cannot be depressed anymore.
Encounter Design: A pressure plate presents a dilemma for characters to resolve, and thus it’s best placed in an area that will either feature some other external pressures (e.g. monsters or another trap) or in an area that the characters will repeatedly pass through (e.g. a “junction room” in a dungeon). Small humanoids may design pressure plates which have a weight threshold allowing Small creatures to pass over without triggering.
Spring Mechanism
A spring mechanism involves a tightly coiled spring, typically tiny and well hidden, that triggers when a trapped object is opened or physically manipulated.
Trap Examples: bear trap, bladed puzzle box, poison needle
Notice: In most cases, a spring mechanism is unnoticeable to the eye. Only a thorough examination of a trapped object – requiring at least 5 minutes and bright light – allows a character to make an Intelligence (Investigation) check to notice the glint of the spring mechanism inside the object.
Disarm: Simply avoiding the trapped object is the best defense, while thieves’ tools are the ideal way to disarm a spring mechanism. Lacking thieves’ tools, a character can attempt to break the object with an attack (referring to the damaging objects rule in the DMG), though if an attack deals insufficient damage to destroy the object then the spring mechanism triggers.
Encounter Design: One of the most iconic traps of D&D is the poison needle hidden in the lock of a treasure chest. Because traps with a spring mechanism are hard to detect, it’s best to either foreshadow them or include a brief window in which the effects can be countered by a well-prepared party (e.g. a poison with an onset time that doesn’t take effect instantly).
Tripwire
A tripwire is typically a thin piece of filament, such as fishing line or a giant spider’s spinneret, stretched across a passage holding a trap in tension. A creature moving into the tripwire while moving at a normal or fast pace triggers the trap.
Trap Examples: crossbow trap, falling net, spiderweb
Notice: A Wisdom (Perception) check allows a character moving cautiously to notice a tripwire. However, a character moving quickly (such as in the heat of combat) automatically triggers a tripwire they are unaware of.
Saving Throw: When a character triggers a tripwire when not moving quickly or in combat, they must make a DC 15 Dexterity saving throw. On a failed save, the tripwire is broken and the trap is triggered. On a successful save, the character’s foot presses into the tripwire but they’re able to stop themselves before breaking it entirely; the character can use an action to Disengage safely from the tripwire, and when disengaging in this way their speed is reduced to 5 feet until the end of their turn.
Disarm: Flying or levitating often avoids a tripwire altogether, as most tripwires are placed low to the ground. Taking an action to attack a tripwire can trigger the trap at a safe distance. An Intelligence (Investigation) check may be necessary to deduce where a tripwire leads to; once that area is located then thieves’ tools can be used to safely end the tension on the tripwire without triggering the trap.
Encounter Design: Because tripwires can be noticed by observant characters, they are best placed where the characters’ guards will be down or external pressure is a factor (in the form of monsters, other traps, or a time limit). As a “minimum investment” trap trigger, tripwires can be set up in dungeons where new occupants have moved in or otherwise have little time to prepare their defenses.
