A bike I rented in Hampi had a very neat lock on it. It was so subtle that I didn’t notice it at first and actually went back to the shop to ask for a lock, at which point the shop keeper showed this neat device to me.
A simple metal bracelet which wraps around the rear wheel. When the metal lever is pushed down, a metal bar slides through the spokes of the tire, so the tire can no longer rotate.
A simple, elegant bike lock. Surely it most be cheap to make. Ideal for a bike rental agency, where the theft you’re looking to prevent comes in the form of opportunists waiting outside popular tourists sites.
Sure, it does not secure the entire bike and a thief could steal then entire bike or use tools to disassemble parts, but since those are less opportunistic thefts and more preplanned, I think this lock is well suited for the work it is assigned.
With a simple turn of the key, the tire is released, and I pedal on.