I agree. There should be a way to mark third-party devices as "My car" so this feature will work in more cars. It works perfectly with my wife's car, which is newer and has a built-in system. However, with my car, which has a third-party bluetooth receiver hooked up to the AUX port, it doesn't work.
Incidentally, you can trigger it manually (if you want) when you get out of your car. Just tell Siri, "Remember where I parked my car."
This is a great tip about Siri! Thanks for including this information!
Some questions:
This is confirmed to work?
Can you do it via Apple Watch?
Can it be triggered manually without Siri?