Message Stones
Wondrous Item,
Uncommon
(cost 450 gp)
Crafting Components
Naturally tumbled river stone
Message stones are a pair of small, smooth stones, carved from two halves of a single rock. While touching one of the stones, you can use an action to cast sending , targeting the creature that carries the other stone. The spell is only cast if a creature is holding the paired stone or it is otherwise touching the creature’s skin.
Once used to cast sending , the stones cannot be used again until dawn of the following day. If one of the paired stones is destroyed, the other loses its magical properties.
Source