Don't have a specific idea on how it'd activate. Maybe by a option when starting a new game, or some sort of object such as a book or simulator thing like in Operation Anchorage of Fallout 3.
They're marked as yellow and when you get hit, a blue diamond shape appears. I put this in accidentally when trying to teleport to my companion Cass. Anyone know a simple 'undo' code which I could insert in?