A second is Julie Fredrickson, who recently sold Stowaway, a venture-backed makeup brand. She had become “a China watcher” out of necessity: It was where she sourced cosmetics. Because she was in the habit of reading supply chain reports, she perked up at early, disturbing reports from Wuhan. “China doesn’t shut down cities,” she said. Ms. Fredrickson was raised in the Bay Area but now lives in Manhattan, where “we enjoy showing off our water bricks in our one-bedroom and the go-bags in the couch.”

And then there’s me. For years, I watched Silicon Valley preppers as an eccentric local tribe — at best goofball hobbyists, at worst elite separatists who fantasized about leaving the rest of us behind to die.

But in January, when I started to notice preppers in an especially high-pitched tizzy about some kind of pneumonia in China, I bought some Lysol. Then some gloves, a couple masks. I found The Prepared and devoured its advice. The site’s central argument made sense: that preparing myself meant I would take up one less spot in the health care system in a crisis. I started to think about what I take for granted. It was kind of a game to play at night, trying to imagine how different parts of my world might falter and how I would stay alive.

Soon I had a prepper box. Inside was flu medicine, headlamps, sardines, gloves, goggles, duct tape, a tarp, a Vipertek VTS-989 stun gun, some whistles. Because of it, I’ve been able to mail supplies to my parents, and I’ve been able to give precious hand sanitizer and high-quality masks to friends. I ended up over-prepping, so I donated the extra to a local clinic.

I have noticed an instinct among those who first mocked Silicon Valley preppers as alarmist is now to call them smug. Certainly, some of them are. But the fact remains that they saw this — or something like it — coming a long ways off.

‘How do I get a gun?’

About a decade ago, Mr. Ramey was living in San Mateo, Calif., and working as the chief executive of isocket, an online advertising start-up. One day, after coffee with a fellow founder, Mr. Ramey opened the trunk of his car, inadvertently revealing something he referred to as his “Get Home Bag,” full of the things he might need if disaster suddenly struck. (“Basic stuff,” he said: first aid kit, food and water rations, radio, multitool, map, compass, jumper cables, a blade to cut someone out of a seatbelt after a crash.)

It was, Mr. Ramey said, the moment that made him “one of the first outed preppers” in the Silicon Valley community. “Other founders and investors started coming to me ad hoc,” he said. “And they’d say, ‘How do I put a kit together?’ And then they’d get really quiet and ask, ‘How do I get a gun?’”