Thank you for the quick reply. What I am trying to do specifically is this: I have a Silent Knight fire alarm panel that has an SBUS OUT, which consists of four contacts, two constant power contacts (positive and negative) and two communications (A and B). I am trying to communicate with an annunciator that is usually hard-wired to these contacts. It does not have to be UL listed for fire alarm as I'm just merely trying to find a way to test the status of the system without having to travel back and forth from the devices to the panel.
I need to emulate this hard-wired connection with some kind of two-way radio system or similar. I am not sure if A and B are digital or analog. It may be possible to drop the two power contacts if I am carrying a 24v source, however the panel supervises all connections so it may complain.
Thank you.