I'd agree 1 way is tat and similar to the DIY stuff available now but scanny 4 stuff was pretty reliable. That was 20 yrs ago though I wouldn't trust it now. I had a tech conversation today about signalling. We used to think 50v pstn and an fsi guaranteed an alarm delivery, we now expect polling and testing the alarm delivery path. Rf is no different if you don't poll you have no idea what might ish be delivered if ever.