www.roadlok.com/
The RoadLoK is installed on your brake caliper and stays there. You carry a pin to lock it.
Typical disc locks can stop a thief from rolling your bike away, but there is a risk of damage. The bike will still roll with a lock on the rotor. The bike is stopped when that lock hits the fork or caliper. Now your bike is safe, but the caliper and fork need to be replaced.
The RoadLoK also stops a thief from rolling your bike away. The difference? There is no movement because the RoadLoK is mounted to your fork. The bike stays exactly where it is. When you return your bike is safe and so are your fork and caliper. With the RoadLoK System there is absolutely no way to damage your bike. Zero.