There's a lot to love about the Mio Fuse, a new wrist-worn activity tracker with an optical heart rate monitor (HRM) that's designed for truly active people, like runners and those who do interval training. Unique features make it undeniably the best and most convenient wrist-worn HRM on the market, and the fact that it also tracks steps, distance, and calories burned makes it useful on rest days, too. For that, plus its very attractive selling price of $149, the Mio Fuse is our Editors' Choice among activity trackers for sports enthusiasts.

That said, the Mio Fuse lacks a few features that people with modest health-improvement goals might want in a tracker, such as a sleep monitor and altimeter to count how many flights of stairs you climb. For that crowd, I recommend the Basis Peak for its all-day HRM and excellent ability to automatically know when you're running, walking, bicycling, and sleeping. Of course, there are many other excellent activity trackers that don't track heart rate at all, which keeps their prices much lower.

What's Unique About Mio Fuse?

The very best aspects of the Mio Fuse relate to its strengths as a heart rate monitor. The HRM is really only meant to be used while you're working out, although you can flip it on and take your resting heart rate if you so choose. During workouts, however, the Mio Fuse has an indicator light that changes color to show you, out of the corner of your eye, your heart rate zone. For example, if the light flashes blue, you know your heart rate is in the low or "very light" exertion zone, maybe between 91 and 110bpm (you can customize the exact cutoff points). Get your heart pumping a little faster, between 112 and 127bpm, say, and the light changes to green.

The purpose of this feature, which debuted in a stand-alone HRM Mio Link, is that you don't need to know your exact heart rate. With other heart rate monitors, you typically only know your heart rate by holding your wrist steady and reading it on a watch face or phone screen, which can slow you down.

Mio Fuse also has a vibration alert, which you can turn off, that causes the band to buzz when your heart rate changes zones, meaning you can still get a good idea of your training zone, even when the band is covered by your sleeves. That's extremely cool.

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Design, Sizes, Colors

The Mio Fuse comes in two colors and sizes: crimson (shown above), which fits large wrists measuring 6.1 to 8.2 inches, and aqua, for wrists measuring 5.9 to 7 inches. The two-pronged watch-style closure on the soft silicone band makes it highly adjustable. Two additional snaps secure the loose end to the band as well.

A red LED dot matrix display shows the time, how close you are to reaching your daily goal, steps, distance, plus other data when in activity-tracking mode. Though old-school, the display is battery friendly, helping the Mio Fuse last six or seven days when used for about one hour of workout time per day. A bonus for swimmers is that the Fuse is one activity tracker that's fully waterproof, to 30 meters, meaning you can shower and swim while wearing it, though the company notes that the HRM may not function well in the pool.

While the Fuse doesn't have any physical buttons, it has two sets of lightly raised dots that act as guides for where its touch capacitive functions work. Touch those dots, and the display illuminates. Touch them again, and you scroll through your data.

There's one more spot in the center of the band where you touch and hold to enable workout mode (a.k.a. activity-tracking). Any time this feature is enabled, the HRM finds your heart rate and displays it, too. Once the Fuse has your heart rate, you touch this center area one more time to begin workout tracking. During workouts, heart rate and pace are added to the display, meaning you can see your actual beats-per-minute reading if you choose, though you always have the indicator lights and vibrations to tell you the zones, too.