Cairos Technologies was among the first to develop a dedicated goal line technology system. The company, based in Karlsbad, Germany, worked in close collaboration with sporting goods manufacturer Adidas but stresses the system is suitable for use with other ball suppliers.
Its solution is similar to that offered by GoalRef; Cairos also uses a magnetic field to track a ball that has a sensor embedded in the middle of the ball bladder. However, the system depends on thin cables with electrical current running through them to be buried 15cm deep in the goal areas and behind the goal lines. Another cable is installed in the goal frame.
When the ball approaches the goal area, the signals from the magnetic field are transmitted to a mobile central processing unit normally located on the side-lines. As with all the other systems described, if the entire ball has crossed the line, an encrypted signal is sent within a second to the referee.
The company stresses that the way the sensor is suspended inside the ball ensures the sensor does not affect the ball's characteristics, even when struck with great force.
— John Walko is a freelance writer and former EE Times editor.