The referee at each of the 52 matches of the FIFA World Youth Championship for the Coca-Cola Cup will be linked to their assistants on the touchline by the pulser system which is now used at all FIFA tournament matches.
There is a button on the flag of each assistant referee on the touchline. If the assistant referee spots an incident behind the referee's back, or of his wishes to attract the referee's attention for any other reason (e.g. to signal a substitution about to take place, or a player injured), he presses the button.
An acoustic signal (whistle) is released and an impulse sent to a strap on the referee's arm, which causes a vibration, thus attracting the referee's attention.
The system, which does not allow for any verbal contact between the referee and his assistants, has been very successful in all matches used so far, including those in last year's Olympic Football Tournaments in the United States.