40d:Trap

(For traps used to catch vermin, see animal trap).

Traps are a reliable and cost-effective method for defending any fortress. Unlike soldiers, they're always on duty, and don't need to be carefully managed. On the other hand, they are immobile and can only lie in wait for foes to walk over them. To build a trap, go to the build->Traps/Levers menu. You'll generally need one mechanism, and at least one other component depending on the type of trap. They can be built indoors or outdoors, and require a level ground square with no other constructions in them. Traps are not triggered by dwarves (except berserk/insane ones), pets, and enemies capable of sneaking, such as kobold thieves. Such creatures will pass over traps without triggering them.

Stone-fall Trap

The simplest trap to construct, a stone-fall trap is essentially a stone suspended up in the air which is dropped on intruders when the trap is triggered. These are a popular defensive measure early on, as the components needed are readily available as soon as you start mining. A single stone trap will kill or severely maim most humanoid enemies although trolls, magmamen and hardier creatures may take two or three to drop. Mythical creatures such as dragons, hydras and titans will take upwards of five or six. After being used they need to be reloaded with another stone, a task which your dwarves will see to automatically. Stone traps can now be built outside.

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Components used: mechanism and an ordinary stone

Weapon Trap

Weapon traps consist of any number of deadly instruments rigged to a mechanism. When an intruder sets off the trap, the weapons spring out and strike the poor sap. You can add up to 10 weapons to a weapon trap, and they will all attack together when set off. This gives the potential for dealing significant amounts of damage at once. There are also special giant weapon parts you can build that are specially designed for use in weapon traps. Unlike stone-fall traps, weapon traps automatically reset after being triggered, ready to splatter the intruder's friends. But there is a (20%?)chance that the trap will become jammed each time it is triggered. A nearby dwarf will automatically clean a jammed trap; this does not require the cleaning labor. If there are weapons that require ammunition in the trap, they will also have to be reloaded occasionally. Weapon traps using bows or crossbows will not require cleaning but do use ammo.

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Components used: mechanism and whatever weapons you want.

Cage Trap

Cage traps capture creatures that set them off in cages. After a creature is captured it's stored, cage and all, in an appropriate animal stockpile. Then the trap is reloaded with another cage. You can do all sorts of fun things with captured creatures. Creatures in cages will be fed periodically. Cage trap is one of the most effective ways to defeat powerful beasts, as even a glass cage can imprison a Colossus. This is expected to be changed.

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Components used: mechanism and a cage.

Upright Spear/Spike

These traps can be utilized in two ways:
1.) They can be positioned in such a way that creatures will fall onto them, such as on the bottom of a channel underneath a retractable bridge.
2.) They can be attached to levers or pressure plates, which when triggered will cause the spikes to extend from the ground and retract back into the ground.

The fact that upright spears/spikes do piercing damage makes them useful against more powerful foes which are most easily killed by damaging their organs. Additionally, the traps' friendly fire means they make extremely useful and effective anti-immigrant traps.

I did some testing, and as far as I can tell they don't cause any extra falling damage. I could be wrong about this as I only tested with wooden spikes and maybe they didn't add enough extra to be noticeable, but I doubt it.

they can, however, be linked to a lever. when pulled, the retract - when pulled again they shoot out doing a moderate amount of damage (5 mid-range wooden spikes pierced both lungs of an elephant and gave it a light liver wound in one shot). The best part is, the lever can be set to repeat which makes the spikes go up and down really fast and causes massive damage to anything walking over them.

stuff does get stuck in them, sort of. corpses will appear as an item inside the spikes 'building' when they are out (the same way mugs and whatnot appear inside workshops when you first make them). retracting the spikes lets the corpse out. I have no idea if a corpse stuck in them stops them from doing damage to other creatures walking over them.

a warning - spikes do friendly fire, and the 5 moderate wooden spikes mentioned above was enough to instagib some elven traders and one of my dwarves in 1 shot. ---- Taken from a forum post by BurnedToast [1]

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Components used: spears or spikes.

Other Traps

You can create even more elaborate traps with imaginative use of pits, pressure plates, levers, grates, supports, water, magma, and whatever else you can think of. Watching those goblins try to find a way out of your drowning chamber as it begins to fill is really quite satisfying.

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