That's only because a driver can turn it off, but not sure if he will get in trouble or not for that one. He hasn't crossed that bridge yet.
Okay, speaking of the driver being able to turn devices off. Modern vehicles are equipped with technology that assists all sorts of activities. They are internet capable, GPS adapted, low jacked and driver assisted. The government or a hacker can hack your vehicle, accelerate it, turn the steering wheel and slam on the brakes causing it roll ... And you are worried about a voice recorder in the cab.
How about we just step back and agree that it would be better to drive a 1970 Nova and take your chances?
It isn't hard for some of us to understand, they have had the capabilities to hear what you are saying for a long time. So the onus is on the person speaking, and how much they trust who is listening. It isn't a matter of whether or not they can hear what you say as much as who wants to hear what you have to say. Think about all those computer savvy folks out there with video cameras and blue tooth devices hooked up to their computers, phones, cars, tablets and freaking watches.
If you ever did have any imaginary privacy, you don't anymore. They were just really poor salesmen and should have sold the drivers on the idea it was for their own safety and convenience.