HKC SABB External Sounder

Hi all, I have a question about the above device that I have sitting in a store room for the last 15 years or more, I've had an idea to use it in a little project I am working on with a pico pi and relay board. I can hook up the Bell + and - terminal to 12v and figured out that if you short BHO to - you can get the siren to operate, unfortunately the only way I can get it to stop is cut the 12v supply momentarily. That's fine I can control all this behaviour with the relays but obviously if the battery is hooked up that doesn't work.

When used with an actual alarm system how does the alarm actually tell the siren to stop, whilst I can certainly make use of this without the battery backup in the siren box it would be nice to have it.

Thoughts ?

Best regards, Peter.