Several approved systems work with cameras that detect the ball and then use specific software to evaluate the footage from all the cameras. This way the system can determine whether or not the ball has crossed the line entirely. Currently licensed systems work with seven cameras per goal installed as high up as possible within the stadium structure.
Several systems operate using magnetic fields. For these systems, cables are placed underground and around the goal and the ball has elements of the technology inside. The interaction between the receptors in the ball and the magnetic fields created through the underground cables allow the software to calculate the exact position of the ball and thus determine when a goal has been scored.