It sounds like the one that Progressive used. They would monitor the time of day you drove, your speed, and acceleration/braking. So if you drove fast, late at night, and braked hard constantly, you would not qualify for a discount but at least they didn't raise your rates. And the best (worst?) part was that you only had to have the thing in your car for 1-3 months, I forget which, but when you were done you sent it back and were free to go back to your original driving style.