Well I found a way to trigger events when a jeep passes though a stream of bullets. No mods whatsoever. It uses "cancelevents" and several relays. This is extremely helpful for setting road-bombs in terrorist RPs. However, I don't really want to show how to do it. Its more fun to figure out yourself. 
easy...
and like meekl said, can be easily bypassed
to event, i basicaly set things up in patterns :D
and a technique i've been thinking about and expirimenting with is to press a number, which fires a relay to a brick, and if you press #2, it fires 2 relays and so on, and making different outputs based on which number was pressed with toggles and cancel events