Ex-AF Security Forces here. There are indeed certain locations where you don’t dare step over the line. Nuclear, chemical weapons sites and places with “one of a kind” resources are immediate, without question, shoot first and recover the bodies later. I have had friends stationed at Groom Lake, and can tell you those people, if they make the attempt, are very likely to have a bad day.
It was a nice sunny day in the summer of 2000. I was working with an Army aviation brigade (Chinooks) up in eastern Wyoming as their SWO. On a whim, we decided to fly up through the Black Hills and have a go around Mt Rushmore and Crazyhorse (Which, BTW, is AWESOME from a helo). We needed to refuel so we stopped off at Ellsworth AFB. We all had to disembark while they refueled-and it was then that some of the Army guys noticed the big pretty red line.
Now - being in the AF (although I was army support my entire career), I knew what a 3' wide red line was for. But - I enjoyed the lecture the crew chief gave the other army guys (mechanics, etc, that were with us) about not crossing the big red line....that if they did...the BEST they could hope for would be to end up face down on the concrete with a few bones broken....and they worse thing that could happen would be that they would be shot...because this was Ellsworth...those were B-1 Bombers...pointing to the planes in the distance...and they were NUCLEAR bombers...and the AF doesn't play when it comes to all things nuclear.
Well...they all thought that was funny...until I...the one AF guy...said: "Uh...he's serious...and they will kill you." It was about that time that a couple of Ford F-150s rolled up and about 6 dudes with M-16's jumped out. They all got about as far away from the red line as they could.
They all stopped laughing. Then it was my turn...:-)