This is something I heard mentioned in passing several (around five?) years ago, so I haven't read the book, nor have I watched the movie. I think I heard about the movie, but I believe it's based on a book. It's really more horror than sci-fi/fantasy, but I guess it could qualify for some sci-fi/fantasy sub-genres... In retrospect, I've thought that what I remember is a lot like "The Hunger Games" and that I may have heard early talks about the film adaptation, but I don't really think so...
Some (young?) teens have been abducted and placed on an island (or somewhere else remote and isolated). (I assume) Only one of them will be allowed to leave, so they'll have to fight and kill each other. To prevent them from co-operating - or hatching a plan to escape - they've all been collared with something akin to shock-collars that will shock them (and possibly kill them) if they spend too much time in proximity to each other.
I believe it's somewhat Saw-like.