TL;DR Want to help test an app on iOS, you’ll need your device(s) UDID’s (Unless you’re using TestFlight)

UDI-what? - Unique Device Id. A long hexadecimal number which uniquely identifies your iOS device.

As well as a serial number, every iOS device has a unique Device Id, or UUID. This identifier can be by developers to create specific build of applications targetted to a given iOS device or set of devices.

Applications built this way can be installed outside of the AppStore and the application simply needs to be copied onto the iOS device via iTunes or Xcode.

How to find the device’s UUID

Due to changes in iOS the UUID can no longer be found programmatically, instead either iTunes or a third party service must be used.

Via iTunes

• Open iTunes (the Mac or PC app, not iTunes on your iPhone).
• Plug in your iPhone, iPod touch or iPad.
• Click its name under the devices list.
• Ensure you’re on the Summary tab.
• Click on the text that says Serial Number. It should change to say Identifier (UDID).
• Select Copy from the Edit menu.
• Your UDID is now in the clipboard, so you can paste it into an email or message.

Install a (temporary) profile

Visit udid.io or SuperUDID from Safari on your iOS device and install the profile (which you can delete after) and email me the UDID.