Because saying "Take note of any unsaved data" after session expired really sucks :) This add-on provides timeout, and action events. To build something useful you have to implement listeners, and for example pop-up a warning, or a countdown window. You might find countdownclock extension useful too. What the extension counts as a user activity (or action)? - It's a user interaction followed by an uidl request. Implementation details. Both timeout and activity tracking is implemented on client side. Timeout is handled with a GWT timer. User action tracked by MOUSEDOWN, KEYDOWN, TOUCHSTART events, and an rpc method called to signal the event to server side. The rpc call is delayed, so it's fired when vaadin sends an uidl request. Timeout modes You can register your timeout listene for an UI, or for a Session. It depends on your needs, wich one to use. For a near-usable example clone from github, and play with the demo module.