Tamper-proof small container

thingiverse

Read the printing instructions carefully and follow them. The end result of this thing is a plastic "brick" 5x25x40 mm, with a hollow interior where you can place important stuff (piece of paper with some code/password/secret for example) with no possibility of getting that thing out without clearly destroying the plastic brick. It won't stop anyone from getting to the inside, but you will know someone has been there. Also, it is not obvious to anyone that there is something inside at all, unless you tell them. It looks like any plastic brick. Because the design is so simple, you may easily copy the cover part (just 1x25x40 mm flat plate) and add something like a domino pattern or whatever to make the brick look even less suspicious.