The National Radio Quiet Zone is not locked down either. There is a public road through Greenbank and the observatory there a very cool visitor center. I can recommend both the coffee and the tours they offer there. The office space for the observatory next door has a locked door, but it is not "as locked down as a military base" by a long shot.

The NRQZ is definitely not locked down, and it's lot bigger than Greenbank too. It's not a super populated region, but it's 13,000 square miles. It is larger than 9 states.

Is is just a sign or is there a formal quiet area enforced by law? I couldn't find anything designating a formal restriction on radio, but I'd be interested in reading about it if there is one. As far as I am aware, the NRQZ is unique in the US.

Back in November I went to Green Bank. 'Outside the wire' (their fence) there really isn't much other than a few signs. Inside the fence they allow nothing but diesel vehicles, phones had to be shut off or if they couldn't they had a faraday cage for them. They do have a truck that hunts down stray RF signals. They shared w/ us that they have found broken electric tooth brushes (which they replaced for free) among the normal stuff that puts out RF. So while it's not RF 'free' (there's cell signal outside the fence area), it is RF reduced. They know of all the signals in the area and filter them out of the results. Really neat place to visit.

Nice article about the area: https://www.bbc.co.uk/news/magazine-32758042

I do also recall an episode of their TV show Click (technology based news show) that covered some form of enforcement that saw a patrol that would monitor and locate (via triangulation) and radio interference - be that leaky microwaves etc.

[EDIT ADD] I think I found the episode of Click in question, though it appear unavailable https://www.bbc.co.uk/programmes/b08450vk

That makes me wonder about electric vehicles, though they'd certainly disallow something like a Tesla since they constantly transmit cellular data.

Electric vehicles emit large amounts of RF from their inverter circuits. If you ever have the chance, try turning on an AM radio while driving in one - you’ll get a very loud and surreal serenade.

Older DC-DC based electric vehicles without inverters ought to be okay.

Don't DC motors have a lot of commutator noise?

Tom Scott went there a few years ago - and in the outer part of the zone, there really isn't a problem having your phone & WiFi turned on. I imagine if you're causing interference, their radio-direction-finding team will pay you a visit. But generally it seems to be much like anywhere else in the US.

https://www.youtube.com/watch?v=64pYTYx_6eU