Session Time out warning

 <script type="text/javascript">
        var sess_pollInterval = 60000;
        var sess_expirationMinutes = 20;
        var sess_warningMinutes = 5;
        var sess_intervalID;
        var sess_lastActivity;

        function initSession() {
            sess_lastActivity = new Date();
            sessSetInterval();
            $(document).bind('keypress.session', function (ed, e) {
                sessKeyPressed(ed, e);
            });
        }
        function sessSetInterval() {
            sess_intervalID = setInterval('sessInterval()', sess_pollInterval);
        }
        function sessClearInterval() {
            clearInterval(sess_intervalID);

        }
        function sessKeyPressed(ed, e) {
            sess_lastActivity = new Date();
        }
        function sessLogOut() {
            window.location.href = 'Logout.aspx';
        }
        function sessInterval() {
            var now = new Date();
            //get milliseconds of differneces
            var diff = now - sess_lastActivity;
            //get minutes between differences
            var diffMins = (diff / 1000 / 60);
            if (diffMins >= sess_warningMinutes) {
                //warn before expiring
                //stop the timer
                sessClearInterval();
                //prompt for attention
                var active = confirm('Your session will expire in ' + 
                (sess_expirationMinutes - sess_warningMinutes) +
                ' minutes (as of ' + now.toTimeString() + '), 
                press OK to remain logged in ' +
                'or press Cancel to log off. 
                \nIf you are logged off any changes will be lost.');
                if (active == true) {

                    now = new Date();
                    diff = now - sess_lastActivity;
                    diffMins = (diff / 1000 / 60);
                    if (diffMins > sess_expirationMinutes) {
                        sessLogOut();
                    }
                    else {
                        initSession();
                        sessSetInterval();
                        sess_lastActivity = new Date();
                    }
                }
                else {
                    sessLogOut();
                }
            }
        }
        initSession();

</script>