If you're over 30, you probably remember being a child, and knocking on the door of your best friend's house to ask their parents if your friend could come out to play. Your parents' friends might sometimes have knocked on the door too, to stop by and visit your parents. Nowadays, if someone turned up unannounced outside your front door, you'd likely either assume there was an emergency, or you were under attack.
If the Wall Street Journal is to be believed, not only are millennials not buying doorbells, they're having them removed from their homes. They expect anyone coming to visit them to call or text before doing so, and so they won't answer the door if they're not expecting guests. They'll just assume it's a salesperson. Who's really to blame for this, though? Millennials, or the invention of the mobile phone?