In our building the internal smoke alarms are unit-only but the external ones (in common areas like lift lobbies) are hard-wired to the fire board and linked to the Fire Brigade – as we discovered when someone left something on their stove and opened their apartment door to clear the resulting smoke. Fire Dept arrived as did the bill for the call-out.
In this case, it sounds like a common property system (albeit within a lot) and that means the OC are responsible both for fixing it and the cost of the call-outs until they do.