I called a Silicon Valley sage, Stewart Brand, the author and entrepreneur whom Steve Jobs credited as an inspiration. In the sixties and seventies, Brand’s “Whole Earth Catalog” attracted a cult following, with its mixture of hippie and techie advice. (The motto: “We are as gods and might as well get good at it.”) Brand told me that he explored survivalism in the seventies, but not for long. “Generally, I find the idea that ‘Oh, my God, the world’s all going to fall apart’ strange,” he said.

To manage that fear, Dugger said, he has seen two very different responses. “People know the only real answer is, Fix the problem,” he said. “It’s a reason most of them give a lot of money to good causes.” At the same time, though, they invest in the mechanics of escape. He recalled a dinner in New York City after 9/11 and the bursting of the dot-com bubble: “A group of centi-millionaires and a couple of billionaires were working through end-of-America scenarios and talking about what they’d do. Most said they’ll fire up their planes and take their families to Western ranches or homes in other countries.” One of the guests was skeptical, Dugger said. “He leaned forward and asked, ‘Are you taking your pilot’s family, too? And what about the maintenance guys? If revolutionaries are kicking in doors, how many of the people in your life will you have to take with you?’ The questioning continued. In the end, most agreed they couldn’t run.”

Monetary disaster investors believe the Federal Reserve system is fundamentally flawed. Newsletters suggest hard assets of gold and silver bullion, coins, and other precious-metal-oriented investments such as mining shares. Survivalists prepare for paper money to become worthless through hyperinflation. As of late 2009 this is a popular scenario.[37][38][39][40] Many will stockpile bullion in preparation for a market crash that would destroy the value of global currencies.

I asked Hoffman to estimate what share of fellow Silicon Valley billionaires have acquired some level of “apocalypse insurance,” in the form of a hideaway in the U.S. or abroad. “I would guess fifty-plus per cent,” he said, “but that’s parallel with the decision to buy a vacation home. Human motivation is complex, and I think people can say, ‘I now have a safety blanket for this thing that scares me.’ ” The fears vary, but many worry that, as artificial intelligence takes away a growing share of jobs, there will be a backlash against Silicon Valley, America’s second-highest concentration of wealth. (Southwestern Connecticut is first.) “I’ve heard this theme from a bunch of people,” Hoffman said. “Is the country going to turn against the wealthy? Is it going to turn against technological innovation? Is it going to turn into civil disorder?”

According to Hobel, shelter is your first priority. Lay down cardboard and other materials to insulate yourself from the ground. (Even in summer, the ground can have temperatures that lead to hypothermic conditions.) Use tarps, blankets, pillows—whatever you can find—to build the shelter on that layer. It should be as low to the ground as possible, and you shouldn’t be able to sit up when you’re inside, Hobel says. Other than the airflow you need to breathe, block all openings to keep cold air from coming in. It’s a matter of conserving heat. A lot of people don’t realize that their bodies are heat sources, Hobel says. You’re almost 100 degrees. Trap that heat around you instead of letting it rise in a tall shelter, and you won’t need a fire to stay warm.

Nail your studs together in lengthwise pairs at a 90-degree angle to form braces. This makes them stronger. Then run three or four braces horizontally across every door, hammering the nails from above and below directly into the frame at a 45-degree angle. If you drive them straight in, they're easier to pop out when somebody kicks the door. Use more braces to secure the drywall over the windows. Try to use longer nails and leave a couple inches of each nailhead sticking out for easy removal. — Clint Carter