I would look here for some information Alarm to USB
Some (not too many) years ago as the product was being developed, there was a lot of forum discussion on the interface to some common alarm systems. I seem to remember the interface was RS-485 but the communication codes were not published and need to be reverse engineered.
I personally have not used one of the above devices, simply because hard wired devices gave no benefit over the keypads I could purchase (with the exception of initial programming). More functionality would require a wireless link which I am not comfortable with for entry / fire alarm. This is not a technical issue but one that has to do with how well I sleep at night.