The RC4 (3-wire) transponder is the latest in the line of transponders from MyLaps. The 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 RC4 transponder also gives additional telemetry data such as voltage to the transponder and transponder temperature each time the loop is crossed. This transponder will only work on RC4 decoder boxes with version 4 firmware or higher.