I think I see where the original question comes from. Hill gets dinged on a play and comes hobbling off as the offense lines up, do you expect Williams (or anyone else) to run to the sideline, change helmets, hear the call, communicate the call, get lined up, & recognize his responsibility in a matter of seconds? In that moment, whomever is replacing Hill would be the ideal candidate to have the speaker in his helmet because the call can be made as he's running on the field. Obviously not getting hurt would be option A & Hill remembering to lay on the turf & not come running off the field at any point would be option B, but I'm sure there will be some instances throughout the NCAA where timeouts get burned or the defense doesn't know what to do at the snap - especially early in the season. They could still signal in something in an emergency until another player gets the helmet with the speaker in it, but against HUNH offenses that's going to be difficult to maintain for an entire drive.