Mutil Login Per Account Prevent

So this page https://www.webmasterworld.com/php/3055206.htm states that there is a fix for the multi login per account by pasteing this

#Prevent Membership Fraud
//check if someone is logged in
if (isset($_SESSION['user_id'])) {
//connect to your db
require('../../../connect.php');
/*build query using hirer_id and current_session_id, get count. If query comes back with a 1, it means there is a match. A match is good because it means no one else logged in during their session. On the other hand, a 0 indicates that no match, meaning someone else logged in simultaneously. Zeros get the boot of death.*/
$result = mysql_query('SELECT COUNT(*) FROM user WHERE user_id='.$_SESSION['user_id']." AND session_id='".mysql_real_escape_string(md5(session_id()))."'");
$login_status = mysql_result($result,0,0);
//recall 1 is good, 0 is bad
if (0 == $login_status) {
//give them the boot
//this is copied from my logout script
$_SESSION = array(); //destroy the variables
session_destroy(); //destroy the session itself
setcookie(session_name(), '', time()-300, '/', '', 0); //destroy the cookie
echo 'Hey, someone else logged in using your account info which means you get the boot.';
exit();
}
}

In the header. All i get is the header showing the txt no matter where i place it in the header.