Meet the Big Bang Referee 2018 FIFA World Cup Russia smart watch which is now being used by the center referees to assist in the Goal Line Technology
In the past the goal line technology used the Cairos GLT system which has now become obsolete since it was too mechanical. Currently the goal line technology utilizes a 1999 system known as the Hawk Eye. The system basically uses high frame cameras to track the ball and even anticipate its flight path even if some cameras within the system are being blocked. The system runs on an advanced software that helps it with the calculations.

Then The Big Bang Referee 2018 FIFA World Cup Russia smart watch. It runs on the Wear OS (formally Android Wear OS) and has the Intel Atom Z34XX processor.
The Big Bang Referee has a 35.4mm watchface, 400 x 400 AMOLED screen, Bluetooth 4.1, 802.11n Wi-Fi, and “around one day” of battery life from its 410mAh battery.

When the Hawk Eye is combined with the Big Bang Referee then the physical center referee does not need to make the decision to whether a goal has been scored or not neither does he need to wait for the VAR to tell him whether to award a goal or not.
The decision is instantaneous, like triggering a laser. Once the ball passes the goal line the  Hawk Eye system reports to the Hublot Big Bang Referee strapped on the referees hand which at once reflects that the ball is in the net.

This has been the case in the ongoing World Cup. First in the match that Spain played against Portugal when Isco hit the bar. Then in the match that France played against Australia and the ball came out of the goalmouth, but the technology allowed the referee to immediately award the goal.