Per Stormin Mormon:

Until it gets wet and freezes?

Has anybody got experience with the mechanical approach?

In my little fantasy world, I would think that a strong-enough spring
and, maybe, polyethylene moving parts would be pretty much
freeze-proof...

I visualize a wand that gets bent over and is secured by a trigger-like
latch that gets released when the box is opened.

i.e. No moving parts save the latch - and that has to release if/when
the box gets opened.

But that's just my little fantasy world and the Real World does not
always get the word...
--
Pete Cresswell