Wouldn't you want a different siren for smoke? With a burglar alarm
you run into the house and lock the doors... and the other, you run
out...

My alarm gives a separate ring tone if the zone is set to be a fire zone. If
you set it to be a 24h fire zone, you don't need to set the alarm for
protection, either.

I've wired my intruder alarm up to my mains smoke detectors via an optional
relay control output. You get the detector alarms plus the alarm buzzer.
You'll even get the outside bell box going, when I can be bothered to fit
it.

Christian.