SRD:Bracers of Defenselessness

Bracers of Defenselessness: These appear to be bracers of armor +5 and actually serve as such until the wearer is attacked in anger by an enemy with a Challenge Rating equal to or greater than her level. At that moment and thereafter, the bracers cause a –5 penalty to AC. Once their curse is activated, bracers of defenselessness can be removed only by means of a remove curse spell.

Moderate conjuration; CL 16th; Craft Wondrous Item, mage armor, bestow curse; Price 1,200 gp.