AngularJS: how to watch tab selection?

I am using angularjs tab and pane example components

angular.module('components', []).
    directive('tabs', function() {
        return {
            restrict: 'E',
            transclude: true,
            scope: {},
            controller: function($scope, $element) {
                var panes = $scope.panes = [];

                $scope.select = function(pane) {
                    angular.forEach(panes, function(pane) {
                        pane.selected = false;
                    });
                    pane.selected = true;
                }

                this.addPane = function(pane) {
                    if (panes.length == 0) $scope.select(pane);
                        panes.push(pane);
                    }
                },
                template:
                    '<div class="tabbable">' +
                        '<ul class="nav nav-tabs">' +
                            '<li ng-repeat="pane in panes" ng-class="{active:pane.selected}">'+
                                '<a href="" ng-click="select(pane)">{{pane.title}}</a>' +
                            '</li>' +
                        '</ul>' +
                        '<div class="tab-content" ng-transclude></div>' +
                    '</div>',
                replace: true
            };
        }).
    directive('pane', function() {
        return {
            require: '^tabs',
            restrict: 'E',
            transclude: true,
            scope: { title: '@' },
            link: function(scope, element, attrs, tabsCtrl) {
                tabsCtrl.addPane(scope);
            },
            template:
                '<div class="tab-pane" ng-class="{active: selected}" ng-transclude>' +
                '</div>',
            replace: true
        };
    })

SomePage.html

<tabs>
    <pane title="Datos Generales">
        <div n