A simple trap: a victim goes near it, and the arrow shoots out of the trap hidden in the wall. The only catch is this is a proximity trigger, that is, the trap is triggered by the nearness of the victim, not by him stepping on a certain tile or something.
Detect: Per-based Traps at -2.
Disarm: DX-based Traps at -2.
Circumvent: Automatic (don't walk near the trap).
Evade: Hearing allows Dodge.
Effects: 1d-1 impaling.
Rearm: Yes, if you have more arrows.