This CNN article talks about insurance companies installing black boxes on people's cars to monitor their driving habits. Drivers who do so would qualify for a discount on their insurance.
The insurance companies insist that this is fine, because it's completely voluntary, although it doesn't take much of a stretch to see the difference between 'voluntary' and 'mandatory' is all in the size of the discount.
Of course, the weak link in this process is that, according to the article, the device works by plugging into the car's diagnostic port and asking the car for speed information, and works across cars because the diagnostic port is standardized. Which means that a little device that fits between the diag port and the monitoring device could be standardized, too.