How to detect robots and spiders with PHP?

Here is the simple function for detecting spiders and robots. It will return true or false.

function is_bot(){
 
    $bots = array(
        'Googlebot', 
        'Baiduspider', 
        'ia_archiver',
        'R6_FeedFetcher', 
        'NetcraftSurveyAgent', 
        'Sogou web spider',
        'bingbot', 
        'Yahoo! Slurp', 
        'facebookexternalhit', 
        'PrintfulBot',
        'msnbot', 
        'Twitterbot', 
        'UnwindFetchor',
        'urlresolver',
        'Butterfly', 
        'TweetmemeBot');

   foreach($bots as $b){
      if( stripos( $_SERVER['HTTP_USER_AGENT'], $b ) !== false ) return true;
   }
   return false;
 }