Smart scales typically use either Bluetooth or a combination of Bluetooth and Wi-Fi. Wi-Fi scales generally cost more because they require more components to work. They're also much more convenient. To get your daily weigh-ins from a Bluetooth scale to the app for tracking, you need a Bluetooth device by your side. If you leave your companion smartphone, fitness tracker, or running watch in the other room, you're out of luck until it's within Bluetooth range. (Some scales can save a recorded weight until the next sync, but the cheaper ones do not.) A Wi-Fi-enabled scale doesn't have this problem. It syncs your data as long as it has a signal from your Wi-Fi router. In our testing experience, Wi-Fi syncing is also more reliable, whereas Bluetooth syncing fails from time to time.