State Farm is the latest insurer promising fat discounts for anyone willing to install an electronic snoop in their car. Called In-Drive, the voluntary program is similar to Progressive's Snapshot. You stick a device in the vehicle's diagnostic port, usually under the steering wheel (most vehicles from 1996 on have this), and State Farm monitors your driving habits. Participants could qualify for discounts up to 50 percent on their auto insurance premiums if the data shows what good drivers they are, says Kip Diggs, spokesperson for State Farm. So, what does In-Drive track? How far you drive and when, how fast you accelerate and turn, and how hard you brake. In other words, pretty much the same criteria used by Snapshot, which Progressive says can reel in up to a 30percent discount if the motorist is top-notch and doesn't drive too much or during high-accident hours (the worst, the so-called "vampire hours," are from midnight to 4 a.m.). Missy Lundberg, a State Farm spokesperson, says that participants will immediately receive about a 10 percent discount on premiums for liability, medical payments, collision and comprehensive coverage. She added that up to a further 20 percent could be trimmed if you don't go above the national average of 12,000 miles a year. Additional discounts would come over time, depending on how safely you drive and when you drive. Customers can track their performance, and the progress of discounts, at State Farm's website. Progressive's Snapshot users can do the same.