A mercury switch makes a very effective readily available low cost tamper switch regardless of how old tech you or anyone else may think it is. Two switches mounted at right angles makes something damned near impossible to pick up and move without triggering at least one of them and that is when you know they are there.
We use them as event counters in a tilt application at work BTW.
I just recently was talking with someone about Mercury switches and how touchy they are. We were talking about cool and nifty uses for them and they have indeed been used for explosive devices in the past and as touchy as I know they are Ide be damned if Ide walk up and even touch more or less kick (nudge) something I thought maybe a bomb or an exolosive device that could have a switch of this type in its construction all that mercury would have to do is flow on way or the other and BOOM!!!