I had an idea for a "trap" (more of a notification than trap) that involves some wire and empty tin cans. Player/Zed runs over/bumps in to a wire making a rattling noise that alerts the player to the postion of the noise. If anyone would care to add on to my idea, feel free.
This is a bad idea. People could use them as waves in an assault on a location. Say they attack the NW airfield, die, log out, sign back in with another character fully armed and in waiting to attack next.