def start_notify(self, on_change):
<EOL>self._device._notify_characteristic(self._characteristic, on_change)<EOL>self._device._peripheral.setNotifyValue_forCharacteristic_(True,<EOL>self._characteristic)<EOL>
Enable notification of changes for this characteristic on the
        specified on_change callback.  on_change should be a function that takes
        one parameter which is the value (as a string of bytes) of the changed
        characteristic value.