The Davis CarChip ($139-$199) plugs into your car's diagnostic jack and records what's happening. Sometimes this is useful for identifying why your engine light has come on. It allows you to read the diagnostic trouble code--just like the guy at the shop--and even reset the trouble light, if you choose.
Other times, it's a tool for monitoring the antics of the teen-aged driver(s) in your home. You can't always be there in the front seat, but everything you tell the kids how fast they were driving and how many times they hit the brakes hard or accelerated quickly, they'll think you'd been there. (The high-end version, $199, even includes an alarm that sounds when your chosen speed, acceleration, or braking limits are exceeded).
If you have an accident, CarChip will also save information leading up to the crash, which could be useful in reconstructing what happened. Of course, if you're a nuts driver yourself, you'd want to make darn sure the other drivers' lawyers never found out you had one of these in your car.
CarChip connects to your PC's USB port for uploads and downloads.
