For Your Espionage-Laced D&D Campaigns

Yeah, it kinda works like Tim Burton's Batmobile.

Armor of Bracering
Armor (any light, medium, or heavy metal armor), very rare

This armor has 4 charges. After you have donned this armor, you may use your action to expend a charge and command the armor to retract. When retracted, the armor collapses into a pair of decorous wristlets and anklets; its weight in this state is 1 lb and your Armor Class reverts to your normal unarmored AC. Another charge and action may be spent to command the armor to extend back to its original shape. The armor regains all expended charges at midnight.

Or like the briefcase armor...
Except in reverse and with bracers.