Ionic event listener fires on every screen, only want is to apply to one controller

in my ionic application I am binding my using the following code to implement a device back button:

var deregister = $ionicPlatform.onHardwareBackButton(
   function () {
       toastr.warning("Back button pressed");
   }, 100
);
$scope.$on('$pause', deregister);

The function executes when I tap on the back button, but it executes on every other screen as well. I only want it to apply to the controller I am using it in. Is there any way that I can accomplish this? Thank you in advance.

EDIT

The reason that I am trying to implement this is that after the application is installed the first time, my device back button event does not fire if I want to exit the application. Splash page is displayed, login screen shown, then with correct credentials home screen is shown. I clear the history on login and home. On home the back button does not work. When I add the back button event listener, the event is applied on all the screens, not just the controller I use this code in. That is the problem.