A chain lock is a type of security device used to secure doors, gates, or bicycles. It consists of a long, flexible chain that can be looped around an object and locked in place with a padlock or a built-in locking mechanism. Chain locks are popular because they offer versatility and can be used in various situations, providing a moderate level of security. These locks are often made from hardened steel to resist cutting and tampering. While they are not as secure as some other locking mechanisms, such as deadbolts or U-locks, they are lightweight and portable, making them a convenient option for everyday use.