I don't think there are too many stations close to Adelaide that have their siren set up to go off, once the power comes back on....
The Fire Station Interface (FSI) - the box on the wall (not to be confused with the decoder box!) can be programmed to send a pager message to whatever pager(s) you want, to advise of power failures.....
It seems a bit strange to me that the siren goes off when power returns...
However, if the FSI has been programed to do that for some reason, I would presume that the contractors who look after the installs / repairs to FSI / Decoder boxes can reprogram the box for you (it used to be AEC - I haven't had to use them for a while, so I don;t know if they are still the guys who do it)
Speak to either your Regional office, or the comms people at State HQ
Pip