title: How to detect variable change events between controllers
body: <p>I'm making a fairly trivial notification system where I want a main menu (outside ng-view) to display the last activity of the user, from what I've read it looks like a service is best used to communicate between controllers. How should I detect when something happens in controller A <strong>immediately</strong> from controller B. Should I $watch the variable of the service? Or is there an easier way to do this? Or given should I just have a root scope variable and $watch and change that with the controllers?</p>