Is it possible to connect Alarm Panel Pro outputs from two different boards to one siren without a hub and how is this done without external components?
Thanks
Yes, you can do this but I would question why you would want to do this.
To answer your question directly – it’s simple. Just make sure that the two panels are powered by the same 12V power supply so that they share a common ground. Then just wire the black wire to the ALRM terminal on both boards. The red wire to either board’s 12V+
The more important question is – why would you want to do this? The siren does not have to be physically wired to a panel to be triggered by it. Your home automation software should be able to turn on the siren from any trigger, regardless if it initiated on the same panel or not.