I read this and was inspired to suggest today’s invention: a low-weight bike lock.
To secure the bike, the handlebars (grey) would be twisted through 90 degrees so that a bolt (yellow) in the seat could be slid into it and held in place with a normal padlock.
This would encircle a tree or a lampost (brown) and thus resist the removal of the machine.
(Both the handlebars and the seat post would need to incorporate captive flanges as shown, in order to avoid their being removed and the whole system circumvented).