<p><pre><code> //let's check if the guest is already in our system
$check = "SELECT * FROM guests WHERE
`first_name` = '$_POST[first_name]'
AND `last_name` = '$_POST[last_name]'
AND `email` = '$_POST[email]' " ;
</code></pre>
I'm not much of a PHP person, but doesn't this imply you're taking user-supplied POST data and are putting it directly into your SQL? If so, that won't end well.<p>Regarding the actual concept, I saw a place which used an iPad as the signin system for visitor badges, complete with a way to sign your name for NDA purposes if you're there for an interview. It seems sound, assuming you can keep people from messing it up with the home button.<p>That said, I think they had an app, not a web page.