AirPort Extreme/Express, Time Capsule: Where to find the serial number
Summary
Learn where the serial number of an AirPort Extreme, AirPort Express, or Time Capsule is located.
Products Affected
AirPort Extreme Base Station, AirPort Express Base Station, AirPort Base Station (Dual Ethernet), Time Capsule, AirPort Express with 802.11n, Time Capsule (Early 2009), AirPort Extreme (Early 2009)
Time Capsule and AirPort Extreme Base Stations (802.11n)
The serial number is located on a gray strip on the bottom of the device:

AirPort Express
The serial number is located next to the AC power plug:

AirPort Extreme Base Station earlier than 802.11n
The serial number is located on a label affixed to the bottom of the device:

Additional Information
Tip: With AirPort Utility 5 or later, you can also find the serial number of any 802.11n-based AirPort base station (including Time Capsule), or AirPort Express 802.11g. Open AirPort Utility (in the Utilities folder), select your AirPort product, click Manual Setup, click AirPort in the Toolbar, then click the Summary tab.