To make sure the students obey the rules and kill each other, the metal collars around their necks track their positions and will explode if they attempt to remove the collars, or linger in "Forbidden Zones"; randomly chosen areas of the map that increase in number over time, re-sculpting and shrinking the battlefield and forcing the students to move around. The collars secretly transmit sound back to the organizers of the game, allowing them to hear the students' conversations, root out escape plans, and log their activities.