Why do the hid lights blink like a strobe light unless they are left on all the time while driving?

Why do the hid lights blink like a strobe light unless they are left on all the time while driving?
why do the head lights blink like a strobe. Hmmm, maybe it's a old police unit. If lights are blinking like that it is a anti theft device & only will do it siting still. are on all the time just another safety device added to sell a car.