Message from Timeout Forms Authentication

I need to show a message when the session of the cookie ends but I do not know how to do it.

    <authentication mode="Forms">
  <forms loginUrl="~/Home/Login" timeout="10" slidingExpiration="true" name="KeyAuth" />
</authentication>

I thought I would do a modal in the Login view and send a special message to know when it is by timeout and when it is common logout but I do not know how to do it.

Thank you very much already.

Greetings.

I update:

I got a logout by timeout in this way.

    protected void Application_EndRequest(object sender, EventArgs e)
    {
        if ((Response.StatusCode == 302) && Response.RedirectLocation.Contains("?ReturnUrl="))
        {            

        }
    }

in the Globalasax now the problem is that I do not know how to get to the view to show this modal

<div id="dialogboxLogin" class="modal hide fade" ng-class="'modal_dialog'">
    <div class="modal-header">
        <button type="button" class="close" data-dismiss="modal" aria-hidden="true">&times;</button>
        <h3><span>Administración</span></h3>
    </div>
    <div class="modal-body">
        <p>
            <span class="multiline">Su sesion ha expirado</span>
        </p>
    </div>
    <div class="modal-footer">
        <a class="btn btn-close" onclick="javascript: $('#dialogboxLogin').modal('hide');">Cerrar</a>
    </div>
</div>

This modal is in the login view.