Windows:

  1. Connect the device to the PC
  2. Open Windows Device Manager
  3. Expand "Universal Serial Bus Controllers"
  4. Right-click "Apple Mobile Device USB Driver", and click "Properties"
  5. Under the "Details" tab, select "Device Instance Path" in the drop-down
  6. The 40 characters after the last "\" under "Value" is the device's UDID


OS X:

  1. Connect the device to the PC
  2. Click the Apple icon in the Menu Bar
  3. Select "System Information"
  4. Expand "Hardware" and select "USB"
  5. Find and select your device under the "USB Device Tree"
  6. The value listed as the "Serial Number" is not really the device's serial number, but is its UDID