We're going to start off with something simple, and go with a fairly basic trap.
Burning Hands Trap (Spells)
|Trigger: Magical: Visual||Effects: Multiple Targets|
|Save: Rods, Staves, Wands||Duration: Instant|
|Resets: Automatic||Bypass: Selective Trigger|
Description: This trap is disguised as part of statuary. In the center of a room stands a 12' statue of whatever sort of creature (cultists, snake-men, elves, whatever) built the structure the statue is contained within. At each corner of the statue is a serpents head or mouth carved from the same stone the rest of the statue is made from. Each head contains a failing magical sensor that causes the serpent head to spit out a gout of flame when it detects any sort of creature moving in front of it, if that creature is different from the ones that created it. Each sensor has a 90 degree arc of vision, and each is on a corner of the statue. The sensors have a 75% chance of functioning each round (determine randomly each round for each sensor that has a target). This trap works particularly well with another type of encounter in the room (either a combat, or needing to search). When activated, the trap does 2d4+4 of fiery damage in a 120 degree arc, half if a save versus Rods, Staves, and Wands is made. Note that depending on the original creatures, the damage could be changed from flame to another type. Note that the arc of damage is larger then the arc required to trigger the trap.
Detection/Disarming:This trap is particularly difficult to both notice and disarm in the traditional methods. Astute characters who examine the serpent heads from one of the safe spots will see ash and scorch marks in the mouths. Traditional disarming methods take twice as long due to the decayed nature of the magical sensors. Non-traditional disarming methods should have a higher chance of success. (Smashing the serpent statues, covering them up with a black bag).