Mind Sharpener

Ring, uncommon (requires attunement)

The item has 4 charges. When you fail a Constitution saving throw to maintain Concentration, you can take a Reaction and expend 1 of the item’s charges to succeed instead. The item regains dice:1d4|noform|noparens|avg (1d4) expended charges daily at dawn.

Source: Eberron: Forge of the Artificer p. 112