In this book, there are loudspeakers everywhere in the community. There is at least one person whose job is to make announcments over those speakers. I think that there is more than one person, though, because you hear that Jonas got scolded over the speaker for taking a fruit from its proper place. I don't think they would announce that to the whole community.
So, I think that there are different "Speakers" as the announcers are called in different areas. I imagine that there are just plenty of people whose job is to spy on each other and report people doing stuff wrong. I have no proof of that, but that is what makes sense to me.