We have a shared system at our track so you just need to get a transponder. Mylaps I think its called.
Ive used something similar to freelaps in my race car, its basically a beam that you set on a wall and a receiver/screen in the car. Now that I think of it would be kind of trick on a bike, as if gives you a lot of easy to read data (fastest lap, if you are slowing or speeding up, etc). A little bulky for a bike Im sure though.