title: How does Trello show users online/offline/idle state accurately?
body: <p>Trello shows the information of online/offline/idle status very accurately as I personally saw. There are several solutions for tracking users online statuses, and to do so accurately requires a serious overhead. There are also the traditional problems of not knowing if a user closed the browser, disconnected etc. that cause inaccuracy in showing the offline/idle status. For a platform that does not have chat functionality (which, I believe, which would have taken the overhead of tracking users' status and therefore makes the task finally easy) how is Trello achieving this, albeit without much overhead?</p>
  
  <p>Also Trello is able to detect disconnects and resume connection (not so smoothly though).</p>
  
  <p>The Pushing and Polling layer of Trello is described <a href="http://blog.fogcreek.com/the-trello-tech-stack/" rel="nofollow">here</a></p>