After my first car was stolen I went out to design and build an immobilizer system based on these PIC16F84 AlphaCard “smartcards”. Along the way I realized that

After my first car was stolen I went out to design and build an immobilizer system based on these PIC16F84 AlphaCard “smartcards”. Along the way I realized that what matters most is that it is obvious that there is something obscure like that and the real security does not matter. So I ended up with very consciously placed smartcard reader, complete with two blinking LEDs and 12wire rainbow flat IDC cable coming from that. In reality only thing that it did was that the card-present switch activated an relay that was wired in series with fuel pump relay coil. It didn't get stolen and I ended up shoving my drivers license into the slot, which for various onlookers made the “security system” look even more like some kind of high-end technology. Edit: the original idea was that there would be some kind of reader unit that converts the ISO 7816-ish protocol to RS485 and the actual cryptographic challenge-response verification will happen in a unit buried deep inside the engine bay. Well, as long as it is one-off obscure hack, you don't really need any of that.