Steal a person’s watch and get their car too....
If the car feature has the same security level as the Apple Pay feature, it will be disabled when the watch is removed and must be enabled each time you put on the watch via a passcode or Touch ID in the phone.
You know ... on Apple Pay, some people think you can steal a phone and they get to use all the credit cards on Apple Pay. In actuality, no one can even get or see the details and they can’t do purchases either.
And thusly ... one won’t be able to steal an Apple Watch and then take the car.
Apple is pretty darned good at that stuff!