alert.hbs

<div id="alert">
	<div id="flash">
		<button type="button" class="close" data-dismiss="alert" aria-hidden="true">&times;</button>
		<strong>Warning!</strong>
		<span></span>
	</div>
</div>

alert.js

App.AlertController = Ember.Controller.extend({
	alert: false,
	observeAlert: function() {
		if(this.alert != false){
			App.AlertCollectionView.content.pushObject();
			$('#flash').addClass('alert alert-' + this.alert[0] + ' alert-dismissable');
			$('#flash span').text(this.alert[1]);
			$('#flash').fadeIn();
		} else {
			$('#flash').remove();
		}
	}.observes('alert')
});

alert_collection.js

App.AlertCollectionView = Ember.CollectionView.create({
	content: [],
	itemViewClass: Ember.View.extend({
		templateName: 'alert'
	})
});

application.hbs

{{view App.AlertCollectionView}}

router.js

App.AuthFilter = Ember.Route.extend({
	beforeModel: function(transition) {
		if(this.controllerFor('auth').get('isGuest')){
			var alertController = this.controllerFor('alert');
			alertController.set('alert', ['warning', 'You must be logged to view this page.']);
			this.transitionTo('login');
		}
	}
});