Sensor grenades. Motion sensor was a camper's tool.
Campers paid their 60+ bucks too. :)
I dunno, I think the cheapest setup I ever saw was a guy who used the motion sensor and the suppressed Spas in BO. He just ran in circles two-shotting people. Although, I guess if that sounds like a good time...
Protip: If you don't see gorilla coming he's already behind you, lotion bottle in hand. --CaPwnd