YEAH, HE IS RIGHT, THE WAY THOSE WORK IS THE SAME WAY MY JETSKI PICKS UP IT'S SPEED, BASICALLY A MAGNET THAT PASSES PAST SOME STRANDS OF WIRE, PRODUCES SMALL AMOUNTS OF VOLTAGE, WHICH INTERN IS CONVERTED TO GIVE YOU YOUR SPEED, RATHER SIMPLE, I CAN SEE THAT IT WOULD BREAK EASILY, BUT AS FAR AS A MAGNET BREAKING, NOT SO SURE ABOUT THAT