This broad adamantine necklace bears a scarab of the same metal, polished to a mirrorlike sheen.

A scarab of invulnerability provides you with brief but complete protection from all forms of damage. For 1 round after activating the scarab, you are immune to all forms of damage (including ability damage), whether from weapons, spells, psionic powers, poison, environmental effects, or any other cause. The scarab doesn’t protect you from harmful effects that don’t deal damage.
A scarab of invulnerability functions once per day. You must wear a scarab of invulnerability for 24 hours before you can access its abilities. If it is taken off, it becomes inactive until worn for an additional 24 hours.

Prerequisites: Craft Wondrous Item, iron body.
Cost to Create: 20,000 gp, 1600 XP, 40 days.