It's possible it's a faulty keypad. The external shouldn't activate on a tamper when unset. But as you don't have a 100% system it's unknown how it will react
you want an active beam for detection. Take a look at the takex or Optex units. I don't like voice diallers as they are not polled a proper monitoring transmitter would be better imo
Im afraid nothing will work as a zone splitter. If you have the cores then you can go more conventional and use eol. If not your looking at an addressable tech like hkc