No. You can't both have isolated a material for 1000's of years from everything* in its environment that will degrade/contaminate it and have it be exposed for human touch. (* pollutants (SO2, NOx, CO2, Ozone), oxygen, humidity, UV light, visible light, dust, dirt, bacteria, mold, insects, mice, etc. etc. Not to mention the random rat droppings, bat droppings, fallen leaves, pebbles, etc. Not to mention natural temperature variations.) You misuse the term "volatile", I believe. You mean unstable? "Lowest tech" presumes that technology is linear. It. is. not. (Which is lower tech: black powder or penicillin?) The most realistic approach has been mentioned: a trap, perhaps a pressure plate connected to a mechanism that mixes two components. If I were going to build a trap which would work after 1000's of years, and which would explode or ignite after such a long time, I'd use hypergolics (see: https://en.wikipedia.org/wiki/Hypergolic_propellant). For instance, kerosene in one sealed bottle, aniline in a second, and nitric acid (fuming or "white" preferably) in a 3rd. Designing and building such a trap would include (imho) the intention that it be operational for 1000's of years, and that's a problem. At that time scale, seismic motions have to be considered. There would have to be assumptions made about climate and geography. Components would have to be very stable. There's nothing particularly "high tech" as far as aniline or nitric acid. Aniline is a component of coal tar, which itself was "discovered" in 1665 C.E. (after that date physical separation of aniline would have been possible, if needed.) Nitric acid in the 13th Century, although the concentrated form I'm referring to may not have been available until the 1700's. The problem I see is the trap's mechanism. I think it would be difficult to build one which you could be relatively sure would work after 1000's of years, unless kept in a very stable environment. And I know of no realistic way to keep an environment stable for 1000's of years.