public function serialize()
    {
        $device = $this->getDevice();
        $spec = array(
            'browser_type' => $this->_browserType,
            'config'       => $this->_config,
            'device_class' => get_class($device),
            'device'       => $device->serialize(),
            'user_agent'   => $this->getServerValue('http_user_agent'),
            'http_accept'  => $this->getServerValue('http_accept'),
        );
        return serialize($spec);
    }