Normally when I travel, I used National or Enterprise for my rental cars. For some reason this week, my travel gal Cindy booked my car through Hertz. Driving into work this morning, I noticed they had installed a camera in the car to watch me. I had always assumed they would track the car. But having a camera watching me is too invasive. So I taped a piece of paper over the lens. I am guessing it might have a microphone in the car too.
Anyway, if you value your privacy, do not rent from Hertz. I know National does not have cameras or microphones in their cars (yet).
Edit: This evening I will be looking over their NeverLost device to see if I can find the fuse for it to disable it.