Chain locks are a type of security device used to protect bicycles, gates, and other valuables. They consist of a strong metal chain that is often covered in a protective sleeve to prevent scratches. The chain is secured with a padlock, making it difficult for thieves to cut through. Chain locks are popular because they are flexible and can be used in various situations. These locks come in different lengths and thicknesses, allowing users to choose one that fits their needs. While they provide a good level of security, it's important to pair them with other locks, like U-locks, for added protection against theft.