[PHP] Simplest way to detect a mobile device

The code detects a user based on the user-agent string by preg_match()ing words that are found in only mobile devices user-agent strings after hundreds of tests. It has 100% accuracy on all current mobile devices and I'm currently updating it to support more mobile devices as they come out. The code is called isMobile and is as follows:

PHP:

<?php
function isMobile() {
    $isMobile = false;
    if(preg_match('/(android|iphone|ipad|up.browser|up.link|mmp|symbian|smartphone|midp|wap|phone)/i', strtolower($_SERVER['HTTP_USER_AGENT']))) $isMobile = true;
    if((strpos(strtolower($_SERVER['HTTP_ACCEPT']),'application/vnd.wap.xhtml+xml')>0) or ((isset($_SERVER['HTTP_X_WAP_PROFILE']) or isset($_SERVER['HTTP_PROFILE'])))) $isMobile = true;
    $mobile_ua = strtolower(substr($_SERVER['HTTP_USER_AGENT'],0,4));
    $mobile_agents = array('w3c ','acs-','alav','alca','amoi','andr','audi','avan','benq','bird','blac','blaz','brew','cell','cldc','cmd-','dang','doco','eric','hipt','inno','ipaq','java','jigs','kddi','keji','leno','lg-c','lg-d','lg-g','lge-','maui','maxo','midp','mits','mmef','mobi','mot-','moto','mwbp','nec-','newt','noki','oper','palm','pana','pant','phil','play','port','prox','qwap','sage','sams','sany','sch-','sec-','send','seri','sgh-','shar','sie-','siem','smal','smar','sony','sph-','symb','t-mo','teli','tim-','tosh','tsm-','upg1','upsi','vk-v','voda','wap-','wapa','wapi','wapp','wapr','webc','winw','winw','xda','xda-');
    if(in_array($mobile_ua,$mobile_agents)) $isMobile = true;
    if (isset($_SERVER['ALL_HTTP'])) {
        if (strpos(strtolower($_SERVER['ALL_HTTP']),'OperaMini')>0) $isMobile = true;
    }
    if (strpos(strtolower($_SERVER['HTTP_USER_AGENT']),'windows')>0) $isMobile = true;
    return $isMobile;
}