> Imagine if you bought a car from somebody, and they secretly kept a spare key and periodically used your car to run their personal errand.

I wouldn't say this is equivalent to them "running a personal errand". If they were remotely enlisting your device in some computational task, sure.

But modern cars do grant the car company the "keys" to your car:

- Tesla's system - GMC OnStar (since 1996!) - Ford SyncConnect (since 2017) - HondaLink - BMW Assist - VW Car-Net

Even if you don't subscribe to the service they can still remotely access your vehicle...