TomTom Serial numbers are located on the bottom of the device, except for RIDER, which is located on the back of the device.
You can also find your device's serial number using TomTom HOME .
To do so, connect your device to your computer and run TomTom HOME.
Inside HOME click on Help > System Information (Help > Configuration info... for HOME 1.x).

Your TomTom System Information screen will now be displayed. Scroll down, your device's serial number will be listed under Connected device:
