Some cars already have a voice control button on the wheel for their existing system which, if done correctly, is overriden by Siri+CarPlay. Which is really nice when it works.
I’m able to control carplay by just saying “Hey Siri.” Siri’s abilities tend to fluctuate based on what Apple is doing on the server, the phase of the moon and whether I remembered to sacrifice a chicken that morning, but otherwise, it seems to work fine.