When I was talking to a safe installer years ago, he was telling me about how the mechanical high security dial locks used in government facilities are actually designed to be shielded from radiation.

When I asked him why, he said that, apparently, someone discovered a portable X-RAY machine can make figuring out a mechanical combination pretty easy.

This was one of the driving forces behind a shift to electronic locks. X-RAY an electronic lock and all you can see is the circuit boards.