The RC4 Pro (3-wire) transponder is the latest in the line of transponders from MyLaps. The standard RC4 transponder supports car ID numbers so you can have the same transponder number in all your cars, with a different ID for each. The standard RC4 transponder also gives additional telemetry data such as voltage to the transponder and transponder temperature each time the loop is crossed. The RC4 "Pro" edition transponder features all the same features as the standard RC4 transponder, except it is 25% smaller, lighter, all black with black wires, and shortened lead wires.  This transponder will only work on RC4 decoder boxes with version 4 firmware or higher.