Honestly I didn’t know that fire alarm speakers could be used as PA speakers until I saw twoplyboy do it on a system in one of his videos on his channel and even then I thought it was only a Canadian thing until I took a closer look at the panels at my college when they replaced the 4051 horns son 4050-80s there with SpectraAlert speaker/strobes and they had a microphone attached to the panel. Though the college has its own PA system that it uses for announcements and they don’t use the microphone in the panel.