Rare Wondrous Item (Bracelets), Requires Attunement 

Shared Bond. While you are wearing one of these magical bracelets and your familiar or beast companion is wearing the other, you two become magically bonded.
While bonded, when either you or your bonded creature are targeted by a spell or magical effect, you can spend your reaction to make the other the target of the effect as well, even if the original range and target of the spell is only “self”. 

Once per short rest when your bonded creature is brought to 0 Hit Points, you can decide to spend one of your hit dice to bring them to 1 Hit Point instead