In my brigade, we have instigated a policy for this fire season to set the station siren off for every call involving a report of a bushfire in our area...regardless of time of day or night...
We also set our siren off for urgent calls, where crews are required ASAP - things like reports of serious crash, building fires etc..... ( and the siren becomes important when at least 9 active fire fighters often miss the pager messages, due to pager coverage issues...but that's another story)
The only "complaint" we had about our siren was from a lady who asked that when we test it on a training night, that we don't make it after 8.30pm, as it wakes up her kids.....not really an unreasonable request!!
Pip