Sitewide message module provides functionality to display urgent message to all users. Originally was created for the module with a lot of Ajax when user can stay on the same page for significant period. Sitewide message module is a simple tool which uses periodic polling from client side within small dedicated iframe. Pulled file sitewide_msg.poller.php using limited Drupal bootstrap to minimize the performance overhead. How to use this Sitewide message module Install module according to standard Drupal procedure and enable it. After that you'll be able to configure displaying sitewide messages in two way: - by assigning dedicated block to desired region; - by using in your page.tpl.php new variable $sitewide_msg, sample usage from real project:

  if ($sitewide_msg) {
    echo $sitewide_msg['placeholder'];
  }
  else {
    // optional - to keep spacing when module disabled.
    echo "<div style='padding-top: 1.5em'></div>";
 } 

To send message, as well as to configure polling interval and optional expiration of the displayed message, use screen at admin/config/people/sitewide_msg .