How to detect user's timezone?

Question

I need to know what time zone is currently my users are in based on their IP or http header.

I got many answer regarding this issue, but i could not understood thos

Answer 1

This works fine...

  echo <<
     if (navigator.cookieEnabled)
       document.cookie = "tzo="+ (- new Date().getTimezoneOffset());
   
EOE;
  if (!isset($_COOKIE['tzo'])) {
    echo <<
        if (navigator.cookieEnabled) document.reload();
        else alert("Cookies must be enabled!");
      
EOE;
    die();
  }
  $ts = new DateTime('now', new DateTimeZone('GMT'));
  $ts->add(DateInterval::createFromDateString($_COOKIE['tzo'].' minutes'));