David Kimura PRO said over 5 years ago on UUID in Rails with ActiveUUID :

You could use a UUID for this, but I think that it would probably be a bit overkill.

I would personally just do something like this with SecureRandom.hex (which is part of the ruby core)

        before_create :populate_subscriber_id
        def populate_subscriber_id
            self.subscriber_id = SecureRandom.hex
          end while self.class.exists?(subscriber_id: subscriber_id)