On Interesting Treasure, The Bejeweled Dragonfly
However, if identified, it is difficult to determine what exactly the item is just supposed to do. It appears to provide some sort of protection, but the effect is barely discernible.
However any spell user wearing this or within 10' will not notice but their spells are marginally less effective (hidden -1 point of damage or +1 to opponents saves). The dragon fly is collecting magical energy, and once powered, will become alive, and serve whoever provided the final energy.
Of course, it has a high market value outside of this purpose.
Sale price: 8,000 gp
Sale price to a mage if the faint magic is detected: 14,000 gp