title: How does bootstrap tell that it is a smartphone
body: <p>I know how to use bootstrap, but I'd like to understand the functioning. I recently tried getbootstrap.com on a HTC One, screensize something like 1900x1080. The page displayed just one column and the collapsed navigation.</p>
  
  <p>But as the layout on the front page is using col-sm-4, it should switch to a multicolumn layout beyond 768px. </p>
  
  <p>By what means could bootstrap tell, that I was using a smartphone?</p>
  
  <p>Edit: Just came across this thread again by accident. 
  Using
  alert(screen.width)
  you get a width which the phone seems to send to the server, which is smaller than the actual pixel size. E.g. my Lumia alerts 403px altough technically it has 720px in vertical position.</p>