Flashback: King Abdullah suggested implanting electronic chips in Gitmo detainees

In an unusual concession, made at the conclusion of their conversation, the
King said, "be assured I am fully briefed on the work you are
doing with Prince Mohammed bin Nayef."

¶7. (S) HOW TO TRACK DETAINEES: "I've just thought of
something," the King added, and proposed implanting
detainees with an electronic chip containing information
about them and allowing their movements to be tracked with
Bluetooth. This was done with horses and falcons, the King
said. Brennan replied, "horses don,t have good lawyers,"
and that such a proposal would face legal hurdles in the
U.S., but agreed that keeping track of detainees was an
extremely important issue that he would review with
appropriate officials when he returned
to the United States.

https://wikileaks.org/cable/2009/03/09RIYADH447.html