How did you implement it?
I was writing that comment, and kept thinking of the possible annoying implementations. For example, I probably don't want a notification every single time someone within 1 mile sends a message.
Some seemingly sane ideas off the top of my head, which I think would be useful and not too annoying:
* A timeout, where I get a notification if there is a new message, after a period where no messages were sent near me
* Notification if I send a message with no reply, close the app, and then someone replies
* Notification if there is a particularly active conversation around me