Normally, there is a sign on the side of the freeway. when the watch zone starts. Let's say it take like 5 sec to go from point A to point B at 100km/h. If you do 200km/h, it will take you like 1,5sec and the guys in the airplane will call the patrol that are like maybe 1km further... If there was no one and you didn't get arrested, i'm pretty sure you won't receive a ticket by mail...