Product review (5 stars): works fine.
These work very well for a quick look guide.  They were reading all pink from all blue 24 hours after I put them in the safe, but changed back to nearly all blue after I ran my dehumidifier, so they do work.  And supposedly they can be re-used for...ever?  I have one in each ammo can and one in the safe on top shelf, so it works for a quick read of conditions.  We'll see.