I'm currently using 2 key cable locks without steel jacket, but I'll have to get myself something better, such as a U-lock and/or a scooter chain lock or a steel-jacketed chain, which are said to be more secure. I typically lock the front wheel to the frame to an immovable object, or lock a wheel to an immovable object and use the other lock to secure that wheel to the frame.
Yet all bike locks are vulnerable if the thief has a power tool. An angle grinder can cut any type of bicycle lock.
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