Handcuffs are restraint devices which are designed to lock someone's hands together, making it difficult for them to escape, hurt themselves, or injure someone else. Law enforcement personnel have been using versions of handcuffs in prisoner restraint for hundreds of years; the modern handcuff emerged around the mid-1800s, and numerous new variations started appearing in the late 20th century.
The concept of tying someone's hands together to restrict his or her freedom of movement is probably ancient, given that it is so basic. Early metal handcuffs were simply made from two hinged loops which were designed to lock over the wrists. These handcuffs carried a distinct disadvantage, since they were not adjustable. Prisoners with thin wrists could wriggle out of them, while prisoners with thick wrists often experienced discomfort.
In 1862, W. V. Adams realized that the inclusion of a ratchet would make handcuffs adjustable. He developed the basic design which continues to be used today, consisting of two bracelets connected by a thin length of chain. Law enforcement personnel can snap the ratcheted end of an open bracelet into the other side, which contains a pawl to catch the teeth of the ratchet. The handcuff is tightened as desired and then locked; double lock versions lock the ratchet in place so that the handcuffs cannot be accidentally pulled too tight.
In addition to handcuffs which link with chains, many handcuff producers also make hinged handcuffs, which bring the hands of the prisoner even closer together and reduce the risk of injury from the chain. Others make handcuffs which are linked by a rigid rod. Because of concerns about injuries from the chains on handcuffs, many law enforcement agencies cover the chain with hose or similar flexible piping which will prevent the prisoner from catching skin or hair in the chain.
Many employees of law enforcement agencies carry handcuffs and they are authorized to use them as needed. They are expected to use handcuffs responsibly and with care for the well being of their prisoners, and most are trained in a variety of restraint techniques which are designed to complement the use of handcuffs. By convention, people are typically handcuffed behind their backs, making it more difficult to pick the cuffs and easier to control the prisoner. Many law enforcement officers also make a habit of cuffing with the lock on the outside of the wrist, further hindering someone who might be considering escape because he or she would find picking the lock a challenge.