Not alarming outside at box?

Just checked my optima plus house alarm as we are going away soon. I enter my password, wait for the bleeping to stop,then trigger my sensors to see if it was working,the bleeps stopped after a while as normal so then opened the door to set the sensor off. At the box it started alarming after a short while as normal but the main audio box outside was not going off. I've tried it a few times and the same thing every time, why does it seem as if it is working at the box but not sending the signal to the main alarm outside ?