Detecta el dispositivo móvil y redirige a su versión correspondiente con un sólo código QR

gistfile1.php

<?php

$user_agent = $_SERVER['HTTP_USER_AGENT'];

switch( true ){
  case preg_match('/iphone|ipad/si',$user_agent):
  	$url = 'https://itunes.apple.com/us/app/whatsapp-messenger/id310633997?mt=8';
		break;
		
	case stristr($user_agent, 'android'):
		$url = 'https://play.google.com/store/apps/details?id=com.whatsapp&hl=es';
		break;

	case stristr($user_agent, 'windows phone'):
		$url = 'http://www.windowsphone.com/en-us/store/app/whatsapp/218a0ebb-1585-4c7e-a9ec-054cf4569a79';
		break;
		
	case stristr($user_agent, 'blackberry'):
		$url = 'http://appworld.blackberry.com/webstore/content/2360/?countrycode=ES';
		break;
		
	default:
		$url = 'http://www.whatsapp.com/';
		break;
}

header( 'Location: ' . $url );

?>