Tracking devices, likely with some sort of embedded security device preventing escape. Trying to contain such a large number of people in this sort of space wouldn't be feasible with a physical security force. The risk of losing control would be too high. The tracking device ensures they can retain remote control from a secure location.

[Spoken with a disturbing amount of confidence.]

But there's some interesting information available if you look through the files. I take it you haven't noticed yet?