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.

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