Tailed Beast Sealing

Whenever Naruto Uzumaki entered into a tailed form, the First Hokage's Necklace activated this technique to restrain him. It is unknown if the technique just restrains Naruto until Yamato is able to suppress the Nine-Tails' influence or if it suppresses the influence by itself as the Nine-Tails cancelled the technique by crushing the necklace. It also alerts Yamato to how many tails Naruto develops.