Why doesn't this function work when I know that the IP Address is "true"?

I am trying to append DEV SRV: to the page title (i.e. title tag) if the IP Address matches that of the dev server. I have tried this both in the functions.php file of my child theme and as a standalone plugin

add_filter('wp_title', 'dev_srv_title');
function dev_srv_title($title) {
        $host = $_SERVER['SERVER_ADDR'];
        if ($host =='0.0.0.0') {
                return 'DEV SRV: '.$title;
        }
    return $title;
}