Aegis bracer

A combination of both magic and engineering, this bracer offers great versatility in combat. When you speak the command word the overlapping metal plates that form the bracer are activated and form a metal shield. 

You can use a bonus action to speak the command word and activate or deactivate the shield. When attacked you can also use a reaction to speak the command word.

While activated the bracer serves as a standard shield. While deactivated your offhand is considered empty.

A shield is made from wood or metal and is carried in one hand. Wielding a shield increases your Armor Class by 2. You can benefit from only one shield at a time.

Notes: Bonus: Armor Class, Combat, Warding, Wristwear