My last two cars had button-triggered voice controls, which solves that concern.

IMO physical-world safety measures are underused. Not just because they provide pretty hard barriers to certain attacks, but also because they often exist in a world the human user can notice and verify.

For example, I would prefer to press a fob-button to unlock or start a car, but there are systems out there where thieves simply boost/relay the signal of your keys in order to open and and drive it away.

Sure, there are countermeasures involving complicated speed-of-light timing tricks, but it could have all been avoided with a button.

It solves that concern if the trigger is built in hardware, not if it's software-driven.

Most people already have a phone with a software-controlled microphone in their pocket; that’s generally considered good enough.

For someone who really wants that level of hardware control, they’re probably better served by an older car with less or no computers.

Yup, this is how I use my voice control in the car. It’s on the steering wheel.