The serial number of the Nike + iPod Sport Kit can be found on the back of the receiver. This is the side of the receiver that includes regulatory and product identification markings and corresponds to the back of the iPod nano when the receiver is connected to the iPod. The serial number is 11 characters long.
Note: While the sensor may also have a serial number, you need to use the receiver's serial number if you need a replacement kit or sensor. If you are using a separately purchased sensor with an iPod touch (2nd generation) or an iPhone 3GS, both of which do not require the use of the Nike + receiver, use the serial number of the iPod or iPhone to obtain service.
For more information on the Nike + iPod Sport Kit, see the Nike + iPod Sport Kit User's Guide.