Guardian Emblem

From Tasha's Cauldron of Everything, page 128.

Description
Wondrous item (holy symbol), uncommon (requires attunement by a cleric or paladin)

This emblem is the symbol of a deity or a spiritual tradition. As an action, you can attach the emblem to a suit of armor or a shield or remove it.

The emblem has 3 charges. When you or a creature you can see suffers a critical hit while you're wearing the armor or wielding the shield that bears the emblem, you can use your reaction to expend 1 charge to turn the critical hit into a normal hit instead.

The emblem regains all expended charges daily at dawn.