Pretty sure that only applies to trials, don't have 1 fitted to my sherco but have seen how they fit up & work on other bikes & would fit 1 if we are forced to. Uses a magnetic cap that is attached to the lanyard which you wear around your wrist, when you pull the cap off the switch it lets the contact inside move & breaks the circuit. Have heard that some types have had problems
I'd expect speedway & dirt track to require them to be fitted before vmx & vinduro