line lock,roll control saftey

you pump up the brakes...then hold them, then hold the button, then release it when you want to move....unless you hit the brakes, and held the button again...it won't do anything....it just locks the existing pressure in the brake line
 
In other words -- the pressure comes from the brake pedal, all the linelock does is hold it there. So if you release the brakes and the button and are heading down the track, pressing the button again will simply hold the pressure that is currently on the front brakes (zero) -- which means it won't do anything.