def register_endpoint(self, endpoint, handler):
return self.event_handler.register_handler((_EventType.Watch, endpoint), handler)<EOL>
Register a handler for a message received from the Pebble.

:param endpoint: The type of :class:`.PebblePacket` that is being listened for.
:type endpoint: .PacketType
:param handler: A callback to be called when a message is received.
:type handler: callable
:return: A handle that can be passed to :meth:`unregister_endpoint` to remove the handler.