This isn't exactly what you might've been looking for, but in de_nuke i think they make the sirens go off by having an output on one of the models that breaks (a crate of some sort) that triggers the lights, so what you would do is:
Event: Target: parameter:
OnBreak spinner1(func_rotating) rotate
OnBreak spinlight1(point_spotlight) on
OnBreak spinlight2(point_spotlight) on
The bomb blast would of course break the crate, and to prevent people from braking the crate by shooting it, put a blockbullets all the way around it. Hope this helps.







