GoalRef uses a microchip implanted in the ball and low magnetic waves around the goal.

CNN: Over the line: Goal tech to be used at 2014 World Cup

Both Britain-based Hawk-Eye and Germany's GoalRef transmit their findings to devices that can be worn on officials' wrists.

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However, both GoalRef and Hawk-Eye's technology must now pass a stadium test before either system can be used in a match.

CNN: FIFA awards goal-line technology licenses

GoalRef, meanwhile, uses a magnetic field and a special ball to determine whether a ball has completely crossed the line or not.

CNN: Goal-line technology enters final testing

British firm Hawk-Eye, which already provides services to tennis and cricket, and German company GoalRef were both granted permission by FIFA following successful trials last year.

CNN: EPL to introduce goal-line technology next season

GoalRef has been developed by German research institute Fraunhofer and involves using magnetic strips inside the ball to detect whether or not it has crossed the goal line.

CNN: FIFA awards goal-line technology licenses

Following a tender process that began in February and involved presentations to FIFA as well as visits to some of Brazil's leading stadiums, the companies that missed out were CAIROS, GoalRef and Hawk-Eye.

CNN: Latecomer wins FIFA goal-line tech deal

While both CAIROS and GoalRef use magnetic fields around the goal and need to insert a chip in the ball, Hawk-Eye and GoalControl use a 3D imaging system to determine the precise location of the ball.

CNN: Latecomer wins FIFA goal-line tech deal

The International Football Association Board (IFAB) said that two technologies -- the British-designed "Hawk-Eye" system and German one called "GoalRef" -- will be trialed between now and June before a final decision is made in July.

CNN: Goal-line technology enters final testing