Source: Wayfinder's Guide to Eberron

Ring, uncommon (requires attunement)

These rings come in linked pairs. If you possess the Mark of Sentinel, you can use a bonus action to form a link to the creature attuned to the other ring; from then on, whenever that creature suffers damage, they only suffer half of that damage and you take the rest. This effect continues until you end it as a bonus action or until you or the other creature removes their ring. This effect isn't limited by range. A creature cannot be attuned to more than one ring of shared suffering.