You, the consumer, agree to allow Progressive to install a monitor that plugs into your car's onboard diagnostic system. Progressive then monitors how you drive: how far, how fast, how many hard brakes and so on. If Progressive likes what it sees, you can get your bill knocked down by as much as 30% after 30 days. Six months later, you mail the device back and have the opportunity to lock in the discount — permanently. If, on the other hand, Progressive puts you in the naughty category, sorry, no discount.