On a trip to Jeju Island (South Korea), I learnt that villagers in the old days did not have to lock their doors. If they were going out, they just put a wooden post across the entrance to keep animals from entering their houses.
I lived in a village when I was a kid. It wasn't necessary to lock our doors too. We were poor and there was nothing worth stealing. :)
In Daegu city (3rd largest city in Korea), while enjoying a stroll and admiring the beautiful, traditional Korean houses, we noticed we could just push open any door. They were not locked!
It was freezing cold that night. Although it was way past opening hours, this young apprentice didn't lock us out in the cold when we came knocking on its door to buy some medicine for a sick member.
First Commenter - Sgshortstories