Good point, what about asking ref to press some button when the foul is detected. Then, some small watch could vibrate and notify a player. Sounds like a simple enough idea to implement.
I am reminded of when the NHL tried to use a wirelessly trackable puck. It worked until the tech involved wasn't up to the rigors of being slapped around by professional hockey players.
In the same vein, I have some doubts about the ability of a watch to stand up to the forces at play on the field.
NFL (and college football) players already have electronics in their gear- the quarterback has a radio in his helmet, the players have RFID trackers in their pads, and there is one in the ball. Some teams also use wearable GPS athlete monitoring devices like the STATSports Apex [0]. They seem to work.
I imagine that a hockey puck is subjected to much harder acceleration than a football, never mind a player, due to the nature of its collisions with the wall.
