According to BBC's h2g2 (and basically all historians of the period):
There are, in fact, no genuine chastity belts dating from medieval times: all known 'medieval' chastity belts have been produced in the first half of the 19th Century. These fake-medieval chastity belts are too heavy and the workmanship is too crude, even for medieval standards. The oldest design for a chastity belt that can be taken seriously dates from the 16th Century - but it's just a design, with no real working models believed to have ever been constructed. The concept of a chastity belt itself is a lot older, but it was usually used in poems in a metaphorical sense. According to Dr Eric John Dingwall, who wrote a deeper study on the subject in 1931, 'the chastity belt probably made its first appearance in ordinary use among the Italians of the period of the Renaissance or perhaps somewhat later.'
Most of the 'medieval' chastity belts on display in museums have been tested to confirm their actual age. As a result, the Germanisches Nationalmuseum in Nuremberg (Nürnberg), the Musée Cluny (officially known as Musée National du Moyen Âge, or the Middle Age Museum) in Paris and The British Museum in London have all either removed the chastity belts from their medieval displays or corrected the date.
