The Beacon of Om
Permanent light-source (radius 4). it burdens its wielder with
aggravation. It cannot be damaged by any means. When worn and activated,
it puts a sigil that blocks undead & demons and prevents summoning,
recharging every 250+d50 turns.
Level 20, Rarity 2, 10.0 lbs, 5000 Gold.

(EyAngband 0.5.2)