Def agree with the wrist idea since that seems to allow functionality but also help to keep them on hand and not get lost so easily. The holo-interface as a keypad for typing also seems the best way to go if we used the wrist concept.

Installing GPS, IPs, and maps of the station would also be good to include in them both for convenience and safety should anyone get lost or go missing, their friends would be able to locate them (or at least follow wherever their ACE is).