Tap the button below on your iPhone/iPad. iOS will prompt to install a temporary profile - tap Allow, then Install. Your UDID will appear on this page automatically, even if iOS shows an "installation failed" message afterward - that's expected and can be ignored, since it just means iOS didn't want to keep the temporary profile installed.
Get my UDIDWaiting for the device to check in… if you see "Profile installation failed" on your phone, just ignore it and check back here.