Abstract: A handcuff includes a pair of arcuate cuff bow arranged to encircle a human wrist. A locking mechanism on one of the cuff bows releasably engages the other bow to secure the bows around a wrist. A fluid actuated cylinder coupled to the locking mechanism releases the locking mechanism when pressurized fluid, such as air, is applied. The fluid actuated cylinder avoids the use of keys, resulting in a more enclosed structure that is more difficult to pick than prior key-based mechanisms. Use of the fluid actuated cylinder further improves security by making ordinary handcuff keys, which are frequently possessed by or available to prisoners, ineffective to open the handcuffs.