Just FYI, Some antique safe were fitted with a binary chemical theft deterrent device. This generally consists of 2 glass vials of one containing sodium hypochlorite and the other nitro methane. The vials are housed in a metal casing mounted on the back or inside of the safe door in line with the combination dial. The idea is that if a thief were to drill out the dial a mechanism would trigger another device that would break the two glass vials thus causing a reaction producing chloropicrin gas a very effective respiratory irritant. Interesting and I would imagine effective deterrent. I have included some photos I took on this response.