Use it to see how fast your teenager was driving last night, make note of severe acceleration or braking, and collect and understand the car's diagnostic codes. There's even a crash recorder. The current model uses a serial port and doesn't work with the handful of cars that use something called the CAN (computer area network) bus - mostly higher-end imports and Ford pickups. A follow-on model due in 2005 should be more compatible and connect via USB.