Football is a game of inches, where just the nose of the ball crossing the goal line can decide a game. That's why the NFL is in talks with Cairos Technology to possibly insert microchips into the balls that would tell refs when they crossed the goal line or the sidelines.
In order to notify the refs when the ball did something like cross the goal line, first down marker or sideline, it would wirelessly transmit to a watch that they would all wear letting them know when it happened.
On the one hand, it could nearly eliminate blown calls. On the other, do we want to remove that element of humanity for the game? I'm personally in favor of the right call every time, but we'll see if the NFL is forward-looking enough to allow this to become a part of the game.