Another wrote to say he’d de-anonymized a man in a loud conversation on the train. He overheard the man’s first name and typed it in combined with the name of the college on his shirt. The student explained in his email to me that even without a last name, he was able to find the stranger’s college major, minor and year of graduation. It helped that in one photo he was wearing the same outfit he wore that day on the train.

People outside my classroom have had experiences similar to those of my students. This week, I tweeted a short thread describing the assignment. “This reminds me of a time at a Starbucks,” a user replied. “This dude was having like a fight with his accountant or something. Kept, loudly, repeating his SSN and full name on the phone. After the third time I wrote it down, and handed it to him.”

Another Twitter user said the exercise reminded her of her mother’s rule to “never use a full name in public,” noting “most people who grew up in a small town had a similar rule, no?” Many probably did. We’ve always known that in a tight-knit community, a bar where everybody knows your name, or a tiny cafe with only three tables, every stray comment made is likely to be overheard and can become a permanent part of the speaker’s reputation. But today you can be in the stands of a major league ballpark and anyone with a smartphone and Google can connect the words you say “privately” in public to other aspects of your identity — your employer, your last vacation, your hobbies, your hometown, your friends.

Does this exercise demonstrate that there’s no more privacy? No, but it does mean that you might have to make it happen for yourself. “If someone wants true privacy in this day and age your actions for achieving it must be intentional,” a user replied to my thread. “You have to work for privacy.”

Networked technology has, as Helen Nissenbaum has written, “altered the meaning of public information” and made privacy in public a value to be protected. The exercise was a reminder that norms, not laws, govern a lot of this day-to-day personal privacy. There’s nothing illegal about Googling the guy loudly talking on his cellphone in line behind you at the grocery store, plugging whatever identifying details he provides into the search engine to learn more about him. But most of us don’t do it — why not? In part because it takes time and energy, but mostly we don’t do it because it’s a little “creepy,” as my students pointed out. The feeling of creepiness is the reaction to a norm being broken, a norm that values our individual ability to be private in public.

Norms are notoriously mercurial and thin protections, but we can do more to educate people and help preserve them, like decreasing the use of internet-connected devices and facial-recognition technology. But perhaps the most significant thing we can do is also the most personal: Treat every place as if it were a small town, and give everyone the privacy that you would give to your neighbor — and that you would want your neighbor to give to you. Also, if you decide to take a call when your plane is on the runway, keep your voice down.

Kate Klonick is an assistant professor at St. John’s University Law School.

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