I had the same thought a few months ago when I moved into a former HMO.
In the end it was easier and more wife friendly to rip out the old system and replace with new interlinked alarms.
I used Fireangel mains-powered and wireless interlinked. Available from Screwfix and Toolstation and the best looking. Aico was the other recommended option.
Steve.mack you can replace the panel you have now with an addressable no problem. You would need to link the loops out in the panel and use the existing radials as spurs. The addressable devices would be monitored, even though you wouldnt be using the FP cable. I could go on and on but if its a route you want to take ill try and help as much as i can.
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