Smart scales introduce estimations for certain stats about your body such as body fat percentage, visceral fat, water, muscle mass etc etc.

Also I can’t cover all smart scales but my Xiaomi Body Composition Scale 2 is definitely HIGHLY inaccurate about most of these stats. Like somehow my muscle mass is the same despite me doing gym + dance now for 4 months now, and I clearly feel the muscle increase. Also this applies for my water percentage as well.