Amulet of Shielding

Upon closer inspection of this fine gold amulet, inlaid amongst intricate patterns and mystic scripts, there appears to be four empty gem settings, which, if inserted in the correct order, would latch on an add to its already significant beauty. Once a day, the amulet's wearer can trigger as part of a reaction a Shield spell, adding +5 bonus to AC until the start of the next turn, including against the triggering Attack, and you take no damage from Magic Missile. No attunement is required.