Smoke alarms, the base station and extra 105db alarm

It was my understanding that the smoke alarms, being connected to the central system (base station) would trigger a "system wide" activation.
To me that meant that if one was triggered, all would sound...to include the base station and external alarm.
Is that not the case? It certainly didn't occur with a smoke alarm test.
Can anyone help explain the way they work?
Thanks!