Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. An event data recorder or EDR is a device installed in some automobiles to record information related to vehicle crashes or accidents. In modern diesel trucks, EDRs are triggered by electronically-sensed problems in the engine, or a sudden change in wheel speed. One or more of these conditions may occur because of an accident. Information from these devices can be collected after a crash and analyzed to help determine what the vehicles were doing before, during and after the crash or event. The term generally refers to a simple, tamper-proof, read-write memory device, similar to the "black box" found on airplanes.