Body composition scales are devices that measure various components of the body, including fat mass, muscle mass, water weight, and bone density. They typically use a method called bioelectrical impedance analysis (BIA), which sends a small electrical current through the body to estimate these components based on resistance. These scales are popular for tracking fitness and health progress, as they provide more detailed information than standard weight scales. Users can monitor changes in their body composition over time, helping them make informed decisions about their diet and exercise routines.