"Amazingly, the trick even works when the phone is just sitting there, its screen black, and sleeping. Say “text by voice” and it wakes up"

I'm pretty sure this is impossible without aggressive battery draw. Altho if you're driving you can be using a car charger. The GPS already makes this neccessary unless you want to risk killing your phone before it guides you home.

It would be nice if they could hook into the 'car dock' app or google maps nav - so that their background service auto launches when those launch. I believe that's possible with some egregious permissions.

Also maybe get the 'charger in' permission and actively listen whenever the phone is plugged in.

Cool idea.