Angularjs watch for change in parent scope

I'm writing a directive and I need to watch the parent scope for a change. Not sure if I'm doing this the preferred way, but its not working with the following code:

  scope.$watch(scope.$parent.data.overlaytype,function() {
    console.log("Change Detected...");
  })

This it logged on window load, but never again, even when overlaytype is changed.

How can I watch overlaytype for a change?

Edit: here is the entire Directive. Not entirely sure why I'm getting a child scope

/* Center overlays vertically directive */
aw.directive('center',function($window){
  return {
    restrict : "A",
    link : function(scope,elem,attrs){

      var resize = function() {
        var winHeight = $window.innerHeight - 90,
            overlayHeight = elem[0].offsetHeight,
            diff = (winHeight - overlayHeight) / 2;
            elem.css('top',diff+"px");
      };

      var watchForChange = function() {
        return scope.$parent.data.overlaytype;
      }
      scope.$watch(watchForChange,function() {
        $window.setTimeout(function() {
          resize();
        }, 1);
      })

      angular.element($window).bind('resize',function(e){
        console.log(scope.$parent.data.overlaytype)
        resize();
      });
    }
  };
});

If you want to watch a property of a parent scope you can use $watch method from the parent scope.

//intead of $scope.$watch(...)
$scope.$parent.$watch('property', function(value){/* ... */});

EDIT 2016: The above should work just fine, but it's not really a clean design. Try to use a directive or a component instead and declare its dependencies as bindings. This should lead to better performance and cleaner design.

I would suggest you to use the $broadcast between controller to perform this, which seems to be more the angular way of communication between parent/child controllers

The concept is simple, you watch the value in the parent controller, then, when a modification occurs, you can broadcast it and catch it in the child controller

Here's a fiddle demonstrating it : http://jsfiddle.net/DotDotDot/f733J/

The part in the parent controller looks like that :

$scope.$watch('overlaytype', function(newVal, oldVal){
    if(newVal!=oldVal)
        $scope.$broadcast('overlaychange',{"val":newVal})
});

and in the child controller :

$scope.$on('overlaychange', function(event, args){
    console.log("change detected")
    //any other action can be perfomed here
});

Good point with this solution, if you want to watch the modification in another child controller, you can just catch the same event

Have fun

Edit : I didn't see you last edit, but my solution works also for the directive, I updated the previous fiddle ( http://jsfiddle.net/DotDotDot/f733J/1/ )

I modified your directive to force it to create a child scope and create a controller :

directive('center',function($window){
  return {
    restrict : "A",
    scope:true,
    controller:function($scope){
        $scope.overlayChanged={"isChanged":"No","value":""};
        $scope.$on('overlaychange', function(event, args){
        console.log("change detected")
        //whatever you need to do

    });
  },
link : function(scope,elem,attrs){

  var resize = function() {
    var winHeight = $window.innerHeight - 90,
        overlayHeight = elem[0].offsetHeight,
        diff = (winHeight - overlayHeight) / 2;
        elem.css('top',diff+"px");
  };
  angular.element($window).bind('resize',function(e){
    console.log(scope.$parent.data.overlaytype)
    resize();
      });
    }
  };
});