Citofono

Italy is made up lots of apartments and very few houses (opposite from America which is mostly houses and fewer apartments.) However, unlike in America, it's not as easy as walking up to a door and knocking if you want to talk with someone - you have to ring their citofono (or doorbell in a sense.) For example, I wanted to show Christie where the elders lived and we took this picture of the label and button that would have to be pushed in order to get to the elders door.
After pressing the button, the person in the apartment would pick up a phone in their home and ask who it was (you, standing at the citofono would be able to hear what they are saying because of a speaker.) You could then let them know who you were and what you wanted. If they knew you they can then let you in by pressing a button which unlocks the door to the stairs to get up to their apartment.

Many of the houses also have this same feature by having an outer gate and a button that must be pushed in order to speak with the owner of the home.

As missionaries, we had a difficult time doing door to door because we would often have to communicate our intent through the citofono which was quickly shutdown. Of course, their were tricks to try and get in to the apartment to knock each door:
1) Ring someone and tell them you're the mail man (mail boxes are usually just inside the apartment door.)
2) Push all the buttons at once causing lots of people to pick up and hopefully someone will just open the door rather than try and figure out what's going on.
3) Ask someone to use their bathroom
4) Wait for someone to go out, then hold the door open just before it closes
Not that I know anything about any of those!