アプリの有無を検出するHtml
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html>
<body>
<script>
window.location = "weixin:";
setTimeout( function(){ window.location="http://itunes.apple.com/us/app/wechat!/id414478124?mt=8";} , 1500);
</script>
</body>
</html>