def on(self):
        """Send the On command to an X10 device."""
        msg = X10Send.unit_code_msg(self.address.x10_housecode,
                                    self.address.x10_unitcode)
        self._send_method(msg)

        msg = X10Send.command_msg(self.address.x10_housecode,
                                  X10_COMMAND_ON)
        self._send_method(msg, False)
        self._update_subscribers(0xff)