Locked. And an alarm turned on while we are away or asleep.
My wife and I are both 67 and it was the same way with parent's housing growing up. We were "latchkey" kids growing up, a term we were not familiar with at the time. We had a house key on a chain around our neck and let our selves into our houses after school because both our parents were at work. I did know some kids whose parents did leave the house unlocked so they could get in after school.
We are one of the few houses on our street without cameras, but we are considering getting them. No really for security reasons, but to monitor the wildlife coming through our yard. Our daughter had cameras on her house and that basically was all they were used for. The watch all the feral cats, possums, racoons, and wild turkeys coming through. Although it was also helpful to see when the trash got picked up or the mail delivered.