I have done work at a number of dark sites over the decades, nothing allowed in at all, no cell phones, no USB's, and they even had their own models of our test equipment for me to use to troubleshoot with so they knew they were clean. When I would go into the control rooms at NSA, CIA, FBI, DNI etc. they patted you, wanded you, and the only thing you took in was your clothes and your brain, everything else was locked up outside.