A bicycle lock is necessary to ensure the safety of your vehicle by limiting mobility. It can be attached to a wheel, to a frame, or to improvised objects - a post, a tree, a fence, etc. People often buy a cheap bike lock without thinking about the consequences. There are various options in quality, design and material they are made of.
The ordinary lock consists of a long cable in a plastic sheath. It’s light and does not take up much space. But it can be easily broken with wire cutters. Recommended only as an additional means of protection (fixing the wheels to the frame).
V - shaped (bracket) - made of a metal rod. It is covered with a special material that protects the frame from scratches. Has a locking mechanism. There is only one drawback - you can not fasten it to everything, but only to a metal fence. But on the other hand, it is reliable, since the steel bow does not lend itself to the influence of even a hacksaw.
A chain (from an improved alloy, iron) is the most optimal solution. Weaknesses include a lot of weight. The thicker, the less chance the thief has. After all, it will take a long time to tinker. And the sufficient length, does not scratch the paint of the bike.
Foldable chain, consisting of several layers covered with polymer material. Ideally combines convenience and reliability.
GPS-alarm, it costs a lot, but you can trace the location in case of theft.
According to the opening method, the bicycle lock can be coded (with a 4-digit number) or locked with a key (flat / cylindrical). In terms of reliability, they are approximately the same. It all depends only on your budget