Returns distance (0, 100) to the beacon on the given channel.
        Returns None when beacon is not found.

def distance(self, channel=1):
        """
        Returns distance (0, 100) to the beacon on the given channel.
        Returns None when beacon is not found.
        """
        self._ensure_mode(self.MODE_IR_SEEK)
        channel = self._normalize_channel(channel)
        ret_value = self.value((channel * 2) + 1)

        # The value will be -128 if no beacon is found, return None instead
        return None if ret_value == -128 else ret_value