is it just me? common sense regarding communication in the apocalypse

i'm a avid fan of the apocalypse genre but recently I've read a couple of novels in a row in general where the government informs the survivors through a radio that they're coming to save the day or telling them a meeting point on where to go so they can pick them up and to hang a red or white flag out their window so they know their survivals in the house. BUT who owns a radio anymore I would think it's really rare so and when they rely on that communication how many people do they really reach And I find it unplausible that everyone knows all the information and that just finding ridiculous in the Arthur says thousands of people were saved and everyone hung a red or white flag out their window Like WHAT?!! And then and then I try to think of ways of where the government can inform everybody where if they didn't have radio they can't go on a megaphone 'cause then they'll attract zombies or monsters or maybe big signs with letters on it but then that's also not plausible or a helicopter and they could be on the megaphone and say it over the city So maybe the author has to stretch out the disbelief So more people are saved ................