Interesting idea, but it would have to be EXTREMELY accurate. I imagine many jewelry items are only off weight wise by small fractions of a gram.
Also if more than one thing was out of the box at a time it could get tricky. I mean if you had items that were 2, 3, 4, 6, and 7 grams in the box, and it reported that you were 10 grams short, does that mean the 3 and 7 items were missing or the 4 and 6? Actually, a very accurate scale might minimize this possibility as it’s unlikely that two different pairs of items would weight exactly the same, but it is possible. And the more items in the box (or taken out of the box) at a time, the most likely it is.
I wonder if a NFC or RFID tag system would work better? You’d need a small enough tag to be able to “hide” it on jewelry. But thinking of my wife’s jewelry, many of her items… rings, pendants, etc. might have a small enough place to stick in a very small tag.
Obviously this would be a lot more expensive than a scale as you’d need the tag sensor as well as a tag for each piece of jewelry. But it would be more accurate.