Your method is fine. Not sure if there is a better way. However, I would make the NetAddr outside the OSCdef, so you aren’t making a new one every time you get a trigger:
BTW 57120 is the default sclang port. If you are trying to send the message to another app, you probably want to use a different port in your NetAddr (and the other app).
I think you can send a ‘/notify’ OSC command from the other application. See Server Command Reference and Server.notify, I don’t remember much of it right now.
[EDIT] Just saw, it was mentioned by rdd above. I think that would be the more direct way.