Sharing data between controllers in Ember

//The Controllers:

    App.AlertsController = Ember.ArrayController.extend({
        sortProperties: ['createdAt:desc'],
        sortedModel: Ember.computed.sort("model", "sortProperties"),
        remaining: function() {
            console.log(this.filterBy('isCompleted', false).get('length'));
            return this.filterBy('isCompleted', false).get('length');
        }.property('@each.isCompleted')
    });

    App.MenuController = Ember.ObjectController.extend({
        needs: ['alerts'],
        alertsBinding: 'controllers.alerts'
    });

//The Route:

    App.AlertsRoute = Ember.Route.extend({
      model: function() {
        return this.store.find('alert');
      }
    });

//The model:

    App.Alert = DS.Model.extend({
        label: DS.attr('string'),
        text: DS.attr('string'),
        createdAt: DS.attr('number'),
        isCompleted: DS.attr('boolean')
    });

    App.Alert.FIXTURES = [
     {
        id: 1,
        label: 'Alert 1',
        text: 'Lorem ipsum dolor sit amet',
        createdAt: Date.now(),
        isCompleted: false
     },
     {
        id: 2,
        label: 'Alert 2',
        text: 'consectetur adipiscing elit',
        createdAt: Date.now() +1,
        isCompleted: false
     },
     {
        id:3,
        label: 'Alert 3',
        text: 'sed do eiusmod tempor incididunt ut labore et dolore magna aliqua',
        createdAt: Date.now()+2,
        isCompleted: false
     }
    ];

//The templates:

        <script type="text/x-handlebars" data-template-name="home">
          <img {{bind-attr src=appInfo.headerImage}} id="header_image" alt="Header Image" />
           {{render "alerts" model}}
          <ul id="home_nav">
            {{render "menu" model}}
          </ul>
        </script>

        <script type="text/x-handlebars" data-template-name="alerts">
            <h4>Alerts: </h4>
        Alerts ({{remaining}})<!-- this returns 3 -->
            <ul class="alert_list">
            {{#each alert in sortedModel}}
                <li>
            {{#link-to 'alert' alert.id}}
                {{alert.label}}
            {{/link-to}}
        </li>
            {{/each}}
            </ul>
        </script>

        <script type="text/x-handlebars" data-template-name="alert">
            <h1>{{label}}</h1>
            <p>{{text}}</p>
        </script>


        <script type="text/x-handlebars" data-template-name="menu">
        <li>
            {{#link-to 'alerts'}}
                Alerts ({{controller.alerts.remaining}})<!-- this returns 0 -->
                Alerts ({{alerts.remaining}})<!-- this returns 0 -->
                Alerts ({{remaining}})<!-- this returns nothing -->
            {{/link-to}}
        </li>
        </script>