there is an external door and then our internal door. the external door is shared with the upstairs flat where joe lives. out internal door has a knocker on it. but it's on the internal door. you can;t get to it without us letting you through the external door. so it doesn't get used. the only person that doesn't live in our house that could get to the knocked without our help is joe what lives upstairs. it's actually HIS knocker but it's on OUR door.
imagine living in a world where everyone had their own door knocker but you could choose what door you put it on.