ASP.NET Push Redirect on Session Timeout

I'm looking for a tutorial, blog entry, or some help on the technique behind websites that automatically push users (ie without a postback) when the session expires. Any help is appreciated

Usually, you set the session timeout, and you can additionally add a page header to automatically redirect the current page to a page where you clear the session right before the session timeout.

From http://aspalliance.com/1621_Implementing_a_Session_Timeout_Page_in_ASPNET.2

namespace SessionExpirePage
{
    public partial class Secure : System.Web.UI.MasterPage
    {
        public int SessionLengthMinutes
        {
            get { return Session.Timeout; }
        }
        public string SessionExpireDestinationUrl
        {
            get { return "/SessionExpired.aspx"; }
        }
        protected override void OnPreRender(EventArgs e)
        {
            base.OnPreRender(e);
            this.PageHead.Controls.Add(new LiteralControl(
                String.Format("<meta http-equiv='refresh' content='{0};url={1}'>", 
                SessionLengthMinutes*60, SessionExpireDestinationUrl)));
        }
    }
}

The SessionExpireDestinationUrl should link to a page where you clear the session and any other user data.

When the refresh header expires, it will automatically redirect them to that page.