Handcuffs are restraint devices designed to secure an individual's wrists close together. 
They comprise two halves, linked together by a chain or hinge. Each half has a rotating part
which engages with a ratchet which is closed around a person's wrist. Without the key, the
person cannot move their wrists more than a few centimetres (inches) apart, making many
tasks difficult or impossible. This is usually done to prevent suspected criminals from escaping
police custody.  

                                                             Old Handcuffs