Detecting mobile web browser

How to detect that the user is using a web browser on mobile phone? The following PHP code can detect it by scanning the user agent string.

if (preg_match('/(up.browser|up.link|mmp|symbian|smartphone|midp|wap|phone|android)/i',
strtolower($_SERVER['HTTP_USER_AGENT']))) {
    $mobile_browser++;
}

if ((strpos(strtolower($_SERVER['HTTP_ACCEPT']),'application/vnd.wap.xhtml+xml')
    > 0) or ((isset($_SERVER['HTTP_X_WAP_PROFILE']) or
    isset($_SERVER['HTTP_PROFILE'])))) {
    $mobile_browser++;
}

$mobile_ua = strtolower(substr($_SERVER['HTTP_USER_AGENT'], 0, 4));
$mobile_agents = array(
    'w3c ','acs-','alav','alca','amoi','audi','avan','benq','bird','blac',
    'blaz','brew','cell','cldc','cmd-','dang','doco','eric','hipt','inno',
    'ipaq','java','jigs','kddi','keji','leno','lg-c','lg-d','lg-g','lge-',
    'maui','maxo','midp','mits','mmef','mobi','mot-','moto','mwbp','nec-',
    'newt','noki','oper','palm','pana','pant','phil','play','port','prox',
    'qwap','sage','sams','sany','sch-','sec-','send','seri','sgh-','shar',
    'sie-','siem','smal','smar','sony','sph-','symb','t-mo','teli','tim-',
    'tosh','tsm-','upg1','upsi','vk-v','voda','wap-','wapa','wapi','wapp',
    'wapr','webc','winw','winw','xda ','xda-');

if (in_array($mobile_ua,$mobile_agents)) {
    $mobile_browser++;
}

if (strpos(strtolower($_SERVER['ALL_HTTP']),'OperaMini') > 0) {
    $mobile_browser++;
}

if (strpos(strtolower($_SERVER['HTTP_USER_AGENT']),'windows') > 0) {
    $mobile_browser = 0;
}

if ($mobile_browser > 0) {
   // MOBILE - do something

}
else {
   // WEB BROWSER - do something else

}