The Spiked Armor can be found in Sword Coast Adventurer’s Guide, page 121.
While wearing this armor, you can use your reaction to give yourself advantage on a saving throw you make against a spell. Once this property is used, it can't be used again until the next dawn.
In addition, while you wear this armor, you can use it to cast Antimagic Field, requiring no spell components. Once this property is used, it can't be used again until the next dawn.
Spiked armor is a rare type of medium armor made by dwarves. It consists of a leather coat and leggings covered with spikes that are usually made of metal.
The wearer has Disadvantage on Dexterity (Stealth) checks.