This elaborately designed ring was specifically designed to kill a king in a heavily guarded castle. So the assassins created the ultimate infiltration tool:

A ring that could open any mechanical lock, without sound, without leaving traces. They put in enough spells to accomplish this difficult mission, but unfortunately the item does not recover any magic - once it is spent, it is gone forever... 
7 charges to cast SILENCE
7 charges to KNOCK open mechanical locks
7 charges to DISPEL Silence

Obiviously, the ring has been forgotten about since it was never used to kill someone (yet).

However: The ring offers a +1 modifier to all DEX-based ability checks.

Notes: Bonus: Dexterity Ability Checks