Correct Conditional Statement - Probably Simple Answer

Hello,

I have a form that has a dropdown selector. That is what I'm keying on to determine how a redirect will work.

I'm passing a value through the query string on submit.

I know its passing the query string, because the links look like:
http://www.XXXXX.com/?s1=Sentry+Mine+Tracking+System
or
http://www.XXXXX.com?s1=Rio+Guest+Tracking+System

But the logic that I got from the forums isn't working and I'm sure its probably just my lack of knowledge about how to write the statement, so the correct page loads

<?php
/*
Template Name: Form Redirect
*/

$s1 = $_GET['s1'] ; // where s1 is what you passed in the query string

if ($s1 == 'Sentry+Mine+Tracking+System')
  wp_redirect('http://www.XXXXX.com/technology/sentry');
else
  wp_redirect('http://www.XXXXX.com/rio');

?>

The second url is the one that is always directed to regardless of the URL/query string.

Thanks,
Louise