Feature request: new or old session?

Hello all, is it possible to get a function something like session_timed_out() ? So i can see, if i got a session variable in GET/POST, but this session already timed out in Php. Php would create a new session, if i call session_start(), but in some cases i would react on the old (nonexistent) session and maybe redirect the user to a error page or again to the start page. Regards -- ads Andreas Scherbaum