Change the title tag when the user goes to another window/tab.

Change Title Tag OnBlur

window.onblur = function () { document.title = 'Your new HTML Title tag'; }
window.onfocus = function () { document.title = 'The default title tag'; }

Use existing title

// Change Title Tag
var currentTitle = document.title;

window.onblur = function () { document.title = 'Hey, over here.'; }
window.onfocus = function () { document.title = currentTitle; }