AMB make personal transponders that have a unique serial number. They are a little red sensor that goes in your car and every time you go passed the loop (start finish line) it senses your car and counts a lap. It makes for automated race tracking and lap counting, but for very consistant lap timing as well. The consistant lap times aren't quite as critical in off road as it is when we race on road where .1 second a lap can put you half a lap down or more by the end of a 5 minute race.