Non-doorman apartment buildings seem to have a glaring vulnerability: social pressure. Because > 99.9% of the people trying to go in behind you are your neighbo

Non-doorman apartment buildings seem to have a glaring vulnerability: social pressure. Because > 99.9% of the people trying to go in behind you are your neighbors or people visiting your neighbors, not criminals, it's difficult to tell people no. I bet it's possible to get into almost any building in a US city just by wearing a suit and telling people you forgot your keys. Eventually someone will let you in.