Demonstrates the Heartbeat pattern. To see this in action, this app in a second window. You'll see both of your IDs are currently logged in. Close a window and you'll soon see the ID disappear. How does this work? Basically, your browser is sending the server a heartbeat every few seconds to tell it you're still around and active. The server tracks, for each user, its last heartbeat. What you see in the 'Current Users' display is an auto-refreshing SQL result showing users with recent heartbeats (Heartbeat Web Service). (Note: because this is refactored from the basic timeout demo, there's nothing you can do to prevent timing out eventually. The period is 10 minutes here.