Horn of goodness/evil
(Dungeon Master's Guide v.3.5, page 259)
Price (Item Level): 6,500 gp (10th)
Body Slot: — (held)
Caster Level: 3th
Aura: Faint; (DC 16) abjuration
Activation: Standard (manipulation)
Weight: 1 lb.
This trumpet adapts itself to its owner, so it produces either a good or an evil effect depending on the owner’s alignment. If the owner is neither good nor evil, the horn has no power whatsoever. If he is good, then blowing the horn has the effect of a magic circle against evil. If he is evil, then blowing the horn has the effect of a magic circle against good. In either case, this ward lasts for 1 hour. The horn can be blown once per day.
Prerequisites: Craft Wondrous Item, magic circle against good, magic circle against evil.
Cost to Create: 3,000 gp (plus 500 gp for base item), 240 XP, 6 days.