Returns the currently active relay.

        :returns: Returns the running relay number or None if no relays are
                  active.
        :rtype: string

def list_running_zones(self):
        """
        Returns the currently active relay.

        :returns: Returns the running relay number or None if no relays are
                  active.
        :rtype: string
        """

        self.update_controller_info()

        if self.running is None or not self.running:
            return None
        return int(self.running[0]['relay'])