Locking or not locking, it would seem, has more to do with one’s internal geography than with the externals — or, as Ms. Braverman puts it, the stories one tells oneself:

I am a free and easy person who is more concerned that my house is open to any friend who wants to drop by than with possessions. I live in a fine building in which people know and respect one another and there is no need to lock my door. I live in a building in which we are all good friends, and if someone who has a few too many drinks walks in by mistake one night and falls asleep on the couch, it’s a good story that proves what a friendly place this is.

Clay, a 25-year-old college student in Sarasota, Fla., lives in the same three-bedroom house he grew up in. His family never locked the door, and he and his two roommates still don’t. He has often come home to find uninvited friends watching “Monday Night Football” (cool); once he came home to find a friend and his girlfriend using his bed (not cool). “That’s my bed and those are my sheets, ” he said, tossing them out.

But that incident was not enough to persuade him to lock the door. He likes his friends to drop by.

Stephen is a well-traveled New Yorker who works in international public relations and is married with young children. He has spent most of his life in high-security doorman buildings on Park Avenue, and he never locks his door during the day — the only key he carries is the one to his bicycle lock. He enjoys the luxury of not having to bother with a key; it’s one of the reasons he pays that “obscene” $1,700-a-month maintenance fee, he says. He does not consider leaving his apartment door unlocked reckless or irresponsible; his doormen are vigilant and there has not been a robbery in his building in the 10 years he has lived there.

Sarah, a 52-year-old real estate broker who moved to New York 30 years ago, does not have a doorman. She lives on the top floor of what she calls a “cozy” 10-unit brownstone in Brooklyn, where she knows her neighbors and the two entrance doors are always locked. If she goes away for the day, she says, she locks her apartment door, but if it’s just an hour or two, walking the dog, she doesn’t bother.

It’s one less thing to do, and “maybe I am not so afraid, as I am European — German from Munich — where we also left our door open” when she was growing up, she says. “It’s a bit of a habit and maybe a bit of a dare, as I always considered myself lucky.”

The time factor — the notion that it is not necessary to lock if one is leaving the house for an hour or two, or traveling to a nearby town — comes up often with No Lock People, even those who have reason to know better.

Steve is a 39-year-old security consultant who lives with his wife and two children in a ranch house in Nassau County, N.Y. He advises corporations and individuals about security systems; when he travels, he puts his valuables in the hotel room safe and carries a $5 bicycle lock for the balcony doors. There are plenty of lightweight valuables in his home that a thief could quickly make off with: three laptops, two DVD players, his wife’s jewelry. But if he is leaving the house for an hour or two, to pick up his 7- and 11-year-olds at school or to go grocery shopping, he says, he doesn’t bother to lock the door.