public function __construct() {
        log_message('debug','Accessing site_offline hook!');
    }

    public function is_offline() {
        if(file_exists(APPPATH.'config/config.php')) {
            include(APPPATH.'config/config.php');

            if(isset($config['is_offline']) && $config['is_offline']===TRUE) {
                $this->show_site_offline();
                exit;
            }
        }
    }

    private function show_site_offline() {
        $this->load->view('common/header');
        $this->load->view('common/maintenance');
        $this->load->view('common/footer');
    }
}

$allowed_ip = '192.168.1.1'; // Whatever your IP address is

if ($_SERVER['REMOTE_ADDR'] == $allowed_ip)
{
   // Load the site
}
else
{
    // Load the maintenance page
}

$this->config->item('is_offline');

$config['is_offline']