A very simple trap, this one involves running a powerful electrical current through a (conductive, though possibly covered with a non-conductive veneer) metal lock that is unlocked with a (likewise conductive) metal key. Those who know about the trap will know to ensure that they are wearing protective gloves when using the key. Those who are not in the know will suffer the trap’s effects.
This trap can be circumvented accidentally, so it works best outside of environments where PCs might naturally be wearing insulative hand protection. Hot climates and places where the PCs do not expect the intrusion to be investigated (so aren’t worried about fingerprints) are the place for this trap – perhaps it is a locker where a captured villain has stashed some critical files. If PCs are using equipment that can detect electrical current (or naturally have such senses), give them an easy-to-automatic chance to notice the trap; if they have similar abilities to detect magnetic fields, give them a slightly harder shot.