An anti-theft device is installed in a vehicle brake line which carries braking fluid. The device includes a check-valve having first configuration in which it permits fluid flow in one direction and inhibits fluid flow in the opposite direction, and a second configuration in which it permits fluid flow in both directions. The check-valve can easily be switched between the first and second configurations, and can be locked in the first configuration. By allowing braking fluid to flow only toward the wheels, it will be evident that the wheel brakes, once applied, cannot be released.