Solid Matter traps thrust, throw, or dump solid objects into the target area. The simplest of these would be a deadfall, which drops rocks or other heavy objects onto victims. Weapon traps of various kinds are just an elaboration of this basic principal: a weapon is just solid matter in a specific shape, to increase damage or cause specific injuries. A third variant is sand or dust, meant to smother or suffocate victims. Occasionally, Solid Matter traps have a Structural, Motion, or State side effect (blocking a passage, knocking a victim down or into a pit, dumping hot stones into water to heat it up, filling the air with thick dust to reduce visibility.) Deploying solid matter requires either a vent or duct with a shutter or valve on one end, dumping the material into the target area when opened, or a channel or track which the object rests on until propelled out by a spring, hammer/lever, or blast of air or water. The opening or shutter that the object passes through as it enters the area will be visible, discoverable by either slow (Vis/S) or paranoid (Vis/P) inspection, depending on size and concealment; ducts or vents, or hollow compartments for firing mechanisms, are detectable by tapping (Aud/C); the movement of the object after the trap is triggered will probably be audible, depending on size of material (Aud/N through Aud/P.)
Liquid Matter traps spill, squirt or pour liquid into the target area. Simple liquids like water are less likely to cause direct damage from impact, but drowning is still a possibility, as is damage from other liquids like acid. Liquid traps are thus more likely to be used to create water hazards, making travel slow, difficult, or impossible; there are also the side effects of liquids seeping into clothing and containers, to possibly damage scrolls, spellbooks, maps, food, or other items that should be kept dry. Liquids are usually deployed the same as solids, but because they can seep through sand and other particles, liquid outlets can be completely covered, making them hard to find (Tact/C). They can also seep through cracks, which will be easily visible (Vis/N,) but easily mistaken for ordinary stonework. Once triggered, a slow-moving seeping or dripping liquid may be detectable as a spreading damp spot in sand (Vis/S) or a gurgling or dripping sound (Aud/S in most cases.)
Gaseous Matter traps inject gasses into an area. There are two basic types: those that blow gas, possibly to push victims in a particular direction or blow out torches and candles, and those that fill an area with gas to suffocate, poison, or otherwise affect targets. Opaque gasses (or smoke, which is really a solid suspended in air) can be used to obscure vision as well. Gas is deployed in pretty much the same way as liquid, but the gas vents can have tinier openings (Vis/P or worse,) and gas seeping through cracks or sand particles may be visually undetectable if the gas is invisible; there may not even be a sound, unless the deployment is quick (Aud/P even then.)
Flammable Matter traps inject materials that are either on fire now or will soon catch fire. The exact deployment depends on the type of matter, which is usually flaming oil (Liquid) or a flame jet (Gaseous,) but burning coals are also a possibility. Flammable gasses are a good option, since they are invisible and do not need to be lit if the trap building assumes the intruders have torches. If the material is not pre-lit, the ignition source may be detectable (Warm/P, or El/P for some kind of small leyden jar that produces a spark.) If it is pre-lit, the burning substance may produce more heat (Warm/S, for a specific spot) and possibly smoke (Odor/S.)
If the material in a trap has unusual properties, there may be leakage or remnants of a previous victim that can provide clues to the trap's presence or nature: debris (Vis/P;) damp spots in sand (Vis/S, definitely any Tactile search;) odors of poisons or methane (Odor/S or P.) The traditional method to detect poisonous gas is with a small animal like a canary; the animal is affected first, providing a warning of a gas leak.