Amateur Radio

I found the most effective way to get a nerd into ham is: mention that ham radio is in the criteria to become an astronaut. Suddenly they're doing the study courses all on their own. Granted, they have to already be a nerd. ;)

For the non nerds, the prepper angle seems to work with some.

The thing you have to deliver is the "why", not the how. If they've decided they want to learn it, they will.