Step 2: Determine the Trigger and Reset

Now that you have a general idea of what you want your trap to do, you can start defining the specifics. The choices you make here may result in adjustments to the CR and cost of the trap, as given on Tables 2–2 and 2–3. Keep a running total of these adjustments; you’ll need them in Step 4.

Trigger

The trigger element determines how the trap is sprung. Each trigger type is described in detail below.

Location: A location trigger springs a trap when someone stands in a particular square. For example, a covered pit trap typically activates when a creature steps on a certain spot. This trigger is the most common type for mechanical traps.

Proximity: This trigger activates the trap when a creature approaches within a certain distance of it. A proximity trigger differs from a location trigger in that the creature need not be standing in a particular square. Creatures that are flying can spring a trap with a proximity trigger but not one with a location trigger. Mechanical proximity triggers are extremely sensitive to the slightest change in the air. This, of course, makes them useful only in places such as crypts, where the air is unusually still.

The alarm spell functions as a proximity trigger for magic device traps. You can voluntarily reduce the area of the spell to make it cover a smaller area.

Some magic device traps have special proximity triggers that activate only when certain kinds of creatures approach. To build such a trigger, add an appropriate spell (usually a divination) to the trap so that it can differentiate among approaching creatures. For example, a detect good spell can serve as a proximity trigger on an evil altar, springing the attached trap only when someone of good alignment gets close enough to it.

Sound: This magic trigger springs the trap when it detects any sound. A sound trigger functions like an ear and has a +15 bonus on Listen checks. Silent movement, magical silence, and other effects that would negate hearing defeat it. To build a sound trigger, add clairaudience to the trap you’re building.

Visual: This magic trigger works like an actual eye, springing the trap whenever it “sees” something. To incorporate a visual trigger into your trap, add one of the spells listed on the following table. Sight range and the Spot bonus conferred depend on the spell chosen, as shown.

Spell	Sight Range	Spot Bonus
Arcane eye	Line of sight (unlimited range)	+20
Clairvoyance	One preselected location	+15
True seeing	Line of sight (up to 120 ft.)	+30

If you want the trap to “see” in the dark, you must either choose the true seeing option or add darkvision to the trap as well. (Darkvision limits the trap’s sight range in the dark to 60 feet.) If invisibility, disguises, or illusions can fool the spell being used, they can fool the visual trigger as well.

Touch: A touch trigger, which springs the trap when touched, is generally the simplest kind to construct. This trigger may be physically attached to the part of the mechanism that deals the damage (such as a needle that springs out of a lock), or it may not. You can make a magic touch trigger by adding alarm to the trap and reducing the spell’s area to cover only the trigger spot.

Timed: This trigger periodically springs the trap after a certain duration has passed. A sharpened pendulum that sweeps across a hallway every 4 rounds is an example of a timed trigger.

Spell: All spell traps have this type of trigger. The appropriate spell descriptions in the Player’s Handbook explain the trigger conditions for each of these traps.