Bioelectrical impedance or bioimpedance analysis works using a weak current that is sent through your body with electrodes from one foot to the other at different frequencies.

The time it takes for these signals to pass through your body depends on the tissue that they encounter along the way. Adipose tissue (body fat) does not conduct, so it slows down some of these signals. The different signal speeds measured by your scales are then used to calculate your body composition in detail using different algorithms.