Customs Trap     CR 4

Type magical; Perception DC 28; Disable Device DC 28
Trigger proximity; Reset auto
Effect illuminated (as a torch; no save); multiple targets (creatures in a 30-ft.-radius; see text); paralysis (5 rounds; DC 14 Will save negates each round)

Entrances to settlements in the Klavek Kingdom are sometimes manned by tax collectors and customs agents. These civil servants (often rather physically imposing, or flanked by physically imposing assistants) ask visitors if they have anything of value to declare, and may tax them on it—especially in the case of merchants.
Of course, there are plenty of folks who aren’t entirely truthful when confronted with these queries.

One method of helping enforcement along is the customs trap. When a visitor doesn’t declare any valuables at all, the customs trap immobilizes and marks anyone carrying items with an accumulated worth of 100 gp or more passing within 30 feet of it. Usually the embarrassment of being caught in a lie is enough to convince the disingenuous that it’s time to pay up, but if not, the city guard is nearby and more often than not, jail time and a fine aren’t far behind.