Like other Fitbit devices, the Charge 3 takes little effort to set up. It works with Android and iOS devices, and all you need is the Fitbit mobile app to use it. Choose the Charge 3 from the list of devices you can pair via Bluetooth to your smartphone or tablet, and follow the on-screen instructions. After setup, you may want to also edit basic information that the Charge 3 uses when tracking activity, such as your age, height, weight, and the activity metric you care most about (steps, active minutes, etc).
The operating system you choose depends solely on the type of smartphone you have because the smart watch is paired with your smartphone. If you own an Android smartphone, your smart watch should have Android Wear or Tizen. If you own an iPhone, choose an Apple Watch. For example, the Samsung Gear S3 runs Tizen and is compatible with both the Android and iPhone.
Our top pick for most people is the Apple Watch Series 4 with GPS (starting at $399), which has a huge display, ultra-fast processor, Raise to Speak Siri, fall detection and a built-in electrical heart rate sensor for taking on-the-go electrocardiograms. It also runs watchOS 5, which makes the watch even more useful with automatic workout-tracking, offline podcast playback and a Walkie-Talkie voice chat feature.