Smart scales tested for the buying guide.

Fitbit's Aria smartphone can measure weight and body fat percentage, and calculate body mass index (BMI). The scale syncs with the Fitbit app on Android, iOS and Windows Phone. Data can also be viewed on the website.

Under Armour's smart scale is only available as part of a $400 HealthBox bundle. The scale can measure weight and body fat percentage, and calculate body mass index (BMI). Data can be viewed in the Under Armour Record app on Android or iOS.

Garmin's Index Smart Scale is designed for athletes and data junkies. The scale measures weight, body fat percentage, muscle mass, body water percentage and bone mass. Data is synced to the Web and the Garmin Connect app on Android and iOS.

In addition to measuring weight, body fat percentage, and body mass index (BMI), the Withings Smart Body Analyzer will measure CO2 levels, temperature and heart-rate. The scale syncs with Apple Health and the Withings app on Android and iOS. Data can also be viewed on the Web.

The affordable Pivotal Living smart scale will only cost you $40. The budget-friendly scale can measure weight, body fat percentage, body mass index (BMI), lean body mass and Basal Metabolic Rate (BMR), more commonly referred to as your daily resting calorie burn. The scale syncs with the Pivotal Living app on Android and iOS.