As you may have noted, in my drawing there's a PCB, but only for the sake of indicating there's going to be something there. At present I don't have a siren or driver circuit for it. Nor do I know any of the voltages I may eventually employ, as well as how I'm planning on interfacing the detector to the PCB. An Opto seems like a reasonable approach. As for a siren, should I go that route, it'll have to be something that has a long on pulse and a short pulse off so that it acts like a traditional siren. I should include a way to silence the siren should it go off by mistake.