Every iDevice has a UDID, or Unique Device Identifier. This important number is akin to a special serial number specific for each and every one of Apple’s millions of iPhones, iPads, and iPods touch. Although most users never need to access their UDID, it’s crucial for developers and beta testers.
By default, the easiest way to locate an iDevice’s UDID is via iTunes. Plug an activated device into iTunes and select it from the iTunes sidebar or menu bar depending on your version of iTunes and how you have it configured. Here, you’ll see all of the information for your iDevice. Click on your device’s serial number and it will show you the iDevice’s UDID.
Right-click (or control-click) on the UDID and you’ll get the option to copy the value to your clipboard.
Easy, right? But the above steps only work if your device is activated. What if it’s not? Those in the iOS Developer Program know that Apple requires a device running beta software to be pre-registered by assigning its UDID to a developer’s profile. If you try to load a beta version of iOS onto a device that hasn’t been pre-registered, it won’t activate when the installation is complete and you’ll be left with a useless device.
iTunes won’t report the UDID of a non-activated device, and the only apparent option is to downgrade to the public release of iOS, make a note of the UDID, and then reinstall the beta. This is a frustrating and time consuming process.
But there’s good news! Instead of restoring the device back to the previous version of iOS just to get the UDID, Mac Geek Gab listener Ray reports that you can use your Mac’s System Information list to find it, even if the device isn’t activated.
First, power on your iDevice and plug it into your Mac. Select the Apple icon at the top-left of the Menu Bar, hold the Option key on the keyboard, and select “System Information” (this menu entry replaces “About This Mac” when the Option key is depressed).
When the System Information window loads, look under the Hardware section on the left and select the entry for USB. A list of your Mac’s USB ports and any attached USB hubs will appear on the right. Find your iPhone in this list and look at the bottom panel. You’ll see a long string of numbers and letters listed for “Serial Number.” Despite the name, this is not your iPhone’s serial number; it’s the UDID.
You can highlight the number from within the System Information window, copy it to your clipboard and use it to register your device with Apple, your company, or your testing platform.
Note that there are also methods for obtaining a UDID from a locked device by using tools found in Xcode, or by manually accessing a device’s configuration and log files. But this method is much easier, quicker, and accessible to all Mac users.