Today’s invention is a new way to reduce the ease with which thefts of bikes can occur.
Consider the simple case of a fixed-gear machine first.
Both sprockets would have irregularly-spaced teeth, in exact correspondence with the pattern of teeth in the chain, which would be unique to an individual bike.
When an owner leaves his bicycle, he slips off the pedal sprocket and takes it with him.
A thief will be unable easily to substitute for this and would find that even wheeling the bike away will be difficult, due to the loose chain interacting with the rear wheel.
This could be extended to derailleur systems, by removing the two-ring front sprocket.