I’ve drafted a functional outline of immobilizer operations and secure keyfob interactions.
The system optionally provides for a challenge response system to assure that the holder of the keyfob knows a secret, not just how to wallop the owner over the head.
Keyfob operation is wired or wireless. As it already has the hardware included for both modes, it also provides a secure, wireless connection between the keyfob when plugged into the USB port of a computer and the car’s network allowing diagnostics, configuration and vehicle monitoring from a convenient location.
(I must mention the obvious to protect the freedom to use the idea.)