So you tried updating to iOS beta and failed to activate . Now you need the UDID to activate by registering  it on Apple Dev Centre. How do you do it ? Well the easy way is using iTunes [Read more] , but now iTunes wont show the “Device Summary” page of your inactive iPhone since its locked . What you can do is get back to older active firmware [in this case iOS 6.1.4 for iPhone 5] or follow the steps exactly as shown below. We will be adding a video at the end of the article , make sure to read see that  for detailed step by step instructions.

What is UDID ?

It is an Unique Device Identifier that is 40 characters long , used to activate and identify your device by Apple Servers .

Method 1 : Itunes

1. The simplest method of them all . Launch iTunes and connect your device using the USB cable.
2. Now select the connected device on the left hand side of iTunes and click on Summary tab 
3. Click on the phone serial number . This will reveal the UDID as shown below . It is the 40 character UDID identifier that can uniquely identify your device among all the devices apple has manufactured. It uses this identification to send out updates for eligible devices . 
4. To copy this 40 character long UDID you have to click on Edit > Copy UDID . This will copy the udid on your clipboard that you can later paste elsewhere . Watch the video below for mode details

Method 2 : Download Free from AppStore

There is a free app on AppStore that can find your UDID and email it for you . Simply download UDID Sender from iTunes [link] and install it on your device. One click operation to find and send UDID .

Method 3 : Look up for iTunes backup Folder

For this method to work , you must have at-least one backup done on your computer . iTunes would periodically backup your iOS device when you connect it with your computer .

Steps to Find Backup Folder : Windows

1. Remove the hidden folders option on Windows by going to My Computer > Organize > Folder and Search Options
2. Now in this page you have to select View and then choose “Show Hidden Folders” option 
3. Ok , so now all the hidden folders are visible. Go to My Computer again and then in C: Drive go to Users > “your user name” > Appdata > Roaming > Apple Computer > MobileSync > Backup
4. Here you will find the folder that is named by your 40 character UDID number . Copy this number to activate your UDID . 

Steps to Find Backup Folder : Mac OSX

From desktop, select Go > Go To Folder then paste in the following command 

~/Library/Application Support/MobileSync/Backup/ 

You should now see the backed up devices with the folder name as the udid number . Copy the folder name and register it on Apple Dev Centre to get your device activated and start using iOS beta . 

Method 4 : Device Summary via USB identifier

 Steps to Find UDID on Mac :

First, turn ON your iPhone or iPad and connect to your Macbook. 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 pressed ).

Go to Hardware section as shown in the image above 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 40 character long UDID.

Steps to Find UDID on Windows :

1. Right click My computer > Properties > Select Device Manager
2. In the bottom you will see “Universal Serial Bus Controllers“
3. Select Apple Mobile Device USB Driver , right click over it and select Properties 
4. Here you will have to go to Details tab and then Device Instance Path .
5. The 40 characters after the last “\” is your device identifier or UDID number .

Also Read :

• Find UDID Number using iTunes 
• App to Find UDID available on AppStore