PHP判断是不是手机访问的函数

网上找来一个PHP判断是不是手机访问的函数
function is_mobile(){
 $_SERVER['ALL_HTTP'] = isset($_SERVER['ALL_HTTP']) ? $_SERVER['ALL_HTTP'] : '';
 $mobile_browser = '0';
 if(preg_match('/(up.browser|up.link|mmp|symbian|smartphone|midp|wap|phone|iphone|ipad|ipod|android|xoom)/i', strtolower($_SERVER['HTTP_USER_AGENT'])))
  $mobile_browser++;
 if((isset($_SERVER['HTTP_ACCEPT'])) and (strpos(strtolower($_SERVER['HTTP_ACCEPT']), 'application/vnd.wap.xhtml+xml') !== false))
  $mobile_browser++;
 if(isset($_SERVER['HTTP_X_WAP_PROFILE']))
  $mobile_browser++;
 if(isset($_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') !== false)
  $mobile_browser++;
// Pre-final check to reset everything if the user is on Windows
 if(strpos(strtolower($_SERVER['HTTP_USER_AGENT']), 'windows') !== false)
  $mobile_browser = 0;
// But WP7 is also Windows, with a slightly different characteristic
 if(strpos(strtolower($_SERVER['HTTP_USER_AGENT']), 'windows phone') !== false)
  $mobile_browser++;
 if($mobile_browser > 0)
  return true;
 else
  return false;
}
函数就是这个了，使用方法
if(!is_mobile()){
   echo "非手机访问";exit; }