What is the most elegant approach to inform a user that his session has timed out?

Ryan Breidenbach

I think best way is to tell them just that - your session has expired. Maybe not in that technical of a manner, but let them know that because of the dynamic nature of your application, information expires over an extended period of time. Then, recover as much state as you can and redirect them to a page where they can start their process over again.

To see and example of this, go to Amercian Airline's site, begin looking for a flight, and then leave it idle for while. When you try to continue, the site will give you a very polite message explaining that your session timed out.