Ring of X-Ray Vision

From Dungeon Master's Guide, page 193. Found on Magic Item Table G.

Description
Ring, rare (requires attunement).

While wearing this ring, you can use an action to speak its command word. When you do so, you can see into and through solid matter for 1 minute. This vision has a radius of 30 feet. To you, solid objects within that radius appear transparent and don't prevent light from passing through them. The vision can penetrate 1 foot of stone, 1 inch of common metal, or up to 3 feet of wood or dirt. Thicker substances block the vision, as does a thin sheet of lead.

Whenever you use the ring again before taking a long rest, you must succeed on a DC 15 Constitution saving throw or gain one level of exhaustion.