It depends how hard they’re looking for you. It took years to find Ted Kaczynski, for example, because he was so very isolated, and so very careful. He once drove to another state, collected pubic hair from a public toilet, and placed it in one of his devices to confuse forensic analysis. He’d go to other states and fish plastic bags out of the trash, then wrap the bombs in them.
Aside from that, he was intensely asocial and didn’t run his mouth. He also lived in Montana, a state known for its ‘mind your own business’ attitude. He didn’t have any friends. He didn’t use electricity or running water. He spent his days in his cabin, or wandering the woods, occasionally working odd jobs for cash. And we all know how he felt about digital devices.
He was caught, eventually, because when he published his manifesto, his brother’s wife recognized his writing style and ideology. If not for that, he might have gone on for years. And if he hadn’t been a terrorist with an FBI task force hunting him, he would’ve been virtually impossible to find.
Really, the trick to disappearing is both very simple and almost impossible for humans to do: don’t talk. Don’t tell anyone where you’re going. Don’t tell anyone where you’ve come from once you get there. Don’t socialize in general – you’ll accidentally leak information about your origins simply by mentioning innocuous details of your life. Pretending to be mute could be a pretty effective tactic.
Simple right? Yet nearly impossible for a social, verbal animal like a human. Kaczynski just happened to be an extreme loner with little to no desire for human companionship.
It’s harder today of course – surveillance cameras, camera phones everywhere, more centralized digital finance and ID systems. You’d have to sacrifice a lot of modern conveniences to remain undetected. Owning a car is probably a bad idea, unless it’s registered under another name. But there are still places in the world where a more primitive life is possible.