How to Redirect to Another Page when Session Timeout in ASP.NET (when pages contain Ajax UpdatePanel)

<script language="javascript" type="text/javascript">
        function doRefresh(){ javascript:__doPostBack(''); }//window.location.href=window.location.href; }

        function doRedirect(){ window.location.href='login.aspx'; }
        
        function getStyleObject(objectId) {
            // checkW3C DOM, then MSIE 4, then NN 4.          
            if(document.getElementById && document.getElementById(objectId))             
	            return document.getElementById(objectId).style;            
            else if (document.all && document.all(objectId)) 
	            return document.all(objectId).style;            
            else if (document.layers && document.layers[objectId])  
	            return document.layers[objectId];            
            else             
	            return false;            
        }

        function setObjectVisibility(objectId, newVisibility) {            
            var styleObject = getStyleObject(objectId);                        
            if (styleObject) 
            {
	            styleObject.visibility = newVisibility;
	            return true;
            } 
            else             
	            return false;            
        }

        function showUserMessage()
        {
            setObjectVisibility("userMessage","visible");
        }
        
        function hideUserMessage()
        {
            setObjectVisibility("userMessage","hidden");
        }
</script>

<div id="userMessage" style="position: absolute; background-color: white; z-index: 1; 
                        display: block; top: 5px; left: 20px; visibility:hidden; border: 1px solid black;">
                        <table width="400" style="width: 200px; height: auto; 
                            background-color:white;">
                            <tr>
                                <td>
                                    Warning: Within next 3 minutes, if you do not do anything, the system will redirect
                                    to the login page. Please save changed data.
                                </td>
                            </tr>
                            <tr>
                                <td align="right"><asp:Button CssClass="groupButton" ID="btnStillHere" OnClientClick="doRefresh()" Text="OK" runat="server" /></td>
                            </tr>
                        </table>                      
                    </div>

    protected void Page_Load(object sender, EventArgs e)
    {
        CheckSessionTimeout();
    }

    private void CheckSessionTimeout()
    {
        //time to remind, 3 minutes before session end
        int int_MilliSecondsTimeReminder = (Session.Timeout * 60000) - 3 * 60000;
        //time to redirect, 5 miliseconds before session end
        int int_MilliSecondsTimeOut = (Session.Timeout * 60000) - 5;

        StringBuilder sb = new StringBuilder();
        sb.AppendLine("<script language="\"javascript\"" type="\"text/javascript\"">");
        sb.AppendLine("var myTimeReminder, myTimeOut;");
        sb.AppendLine("clearTimeout(myTimeReminder);");
        sb.AppendLine("clearTimeout(myTimeOut);");
        sb.AppendFormat("var sessionTimeReminder = {0};\n", int_MilliSecondsTimeReminder);
        sb.AppendFormat("var sessionTimeout = {0};\n", int_MilliSecondsTimeOut);
        sb.AppendLine("myTimeReminder=setTimeout('showUserMessage()', sessionTimeReminder);");
        sb.AppendLine("myTimeOut=setTimeout('doRedirect()', sessionTimeout);");
        sb.AppendLine("</script>");
        Page.RegisterClientScriptBlock("CheckSessionOut", sb.ToString());

    }

public abstract class SessionPage : Page
{
    protected override void OnLoad(EventArgs e)
    {
        if(Session["SomeSessionIdentifier"] == null)
        {
            Response.Redirect("~/login.aspx");

        }
    }
}
public class MyPersonalPage : SessionPage
{
    //This page only executes to the end if the session is valid
}