Mio Slice

Fitness trackers are changing, and the Mio Slice is at the forefront of that movement. Steps have long been the metric of choice for many, but simply knowing how far you’ve walked or run isn’t really the best indication of how fit you are.

Sure, you could walk 10K every day, but if it’s taking you 8 hours of slow, methodical plodding to do so, you’re not really burning off that much energy.

That’s why the Mio Slice is trying something different. Unlike the Fitbit Charge 2, Misfit Shine 2, or even the Apple Watch 2, this wrist-based fitness tracker puts step count in the shadows and instead makes PAI the metric of choice.

Before you start groaning and giving up on your exercise kick before it’s even started, trust us, this isn’t as complicated as it sounds. What it is, however, is something that could make the Mio Slice the only fitness tracker you should be considering. Potentially.

Mio Slice price and release date

  • Out Now
  • Costs $129/£119 (around AU$170)

Despite tracking things a little differently, when it comes to price, the Mio Slice is just like the masses.

With a $129/£119 (around AU$170) asking price, it’s slightly cheaper than both the Fitbit Charge 2 and Garmin Vivosmart HR, but more expensive than the display-bereft Misfit Ray, a simple steps tracker that can be picked up for just $100/£80/AU$138.

With no GPS but an inbuilt heart rate sensor and basic wrist-based message alerts, however, it’s a price that fits the Slice’s skill set.


  • Boring, basic design
  • Rigid body and firm strap aren’t the most comfortable
  • Four colors and waterproof to 30m

When it comes to looks, the Mio Slice is classic fitness tracker. That's not necessarily a good thing though.

A bland, lifeless combination of plastic, rubber and metal, the Slice is a gadget that falls somewhere between fitness tracker and goth cuff in the looks department. At least the black model we tested does. With navy, ‘stone’ white and sienna (a sort of burnt orange) finishes also available, there are options with a sportier, more lifestyle look.

While they might spruce things up, colors aren’t going to fix underlying problems - the Mio Slice simply doesn’t look that nice. And it’s not particularly comfortable either.

Like the old Microsoft Band 2, everything’s just too stiff and rigid. There’s not enough flex to the Slice’s firm rubbery plastic strap, and the subtle curve to its aluminum and plastic body is too shallow to properly hug the contours of your wrist.

Although being too blocky to ever really feel like a true extension of your arm, it’s during regular daily tasks, such as sat at a desk or eating a meal, rather than vigorous exercise, that the Slice feels most cumbersome.

It’s not a total design dog though. When out running or enjoying a bit of sporting action, the Slice is slim and light enough to forget about. While that doesn’t quite make up for the design shortcomings, it’s arguably the most important element when snapping up a fitness tracker.

That success can be pinned on the device’s compact form factor. There are two strap length options available, meaning there’s a model to fit your wrist, with each lining up at just 1.35cm thick and either 28g for the small version or 29g for the large one.

No, it’s still not going to win any beauty contests, but there are other design triumphs too, namely the wristband’s waterproof skills. Capable of surviving dunks to depths of 30 meters, you can keep the Slice on come swim or shower time.

Sadly, it’s from the good back to the bad, because it’s not just the Slice’s general look that falls short. The device’s design leaves a lot to the imagination when it actually comes to using the thing too.

The integrated OLED display is basic at best, with individual pixels clearly visible. OK, so it doesn’t need to be graphically equal to your phone, but a bit of added sharpness would make mid-run metric tracking a bit easier.

So too would more buttons, as navigating through the Slice’s menus is a bit of a contest. That’s because there are up to 10 menu options (customizable in the app) and just a single button. That means getting where you want to go requires a lot of presses and if you miss your stop, you’ve got to keep going until you loop back around. Not ideal when your arms are flailing around mid-run.

Specs, performance and fitness

  • Prioritizes new PAI fitness metric
  • Integrated heart rate sensor for more accurate fitness tracking
  • Usual steps and calorie counting available

Want to get fit? Walking an extra few thousand steps a day is a solid start, but it’s only going to take you so far. The Mio Slice is aware of this, which is why PAI has become its go-to fitness metric of choice.

Not familiar with PAI? It stands for Personal Activity Intelligence and, instead of relying on steps and motion to judge fitness progress, like the Fitbit Alta and most other trackers, it utilizes your heart rate data to track how much energy you’re exerting and for how long. 

This is then played through a specifically designed algorithm to convert energy exertion into fitness-based PAI points.

It’s not the same levels for everyone, either, but instead is a system tailored to you. During the setup process, you’re asked to input your age, weight and height. This is used to determine where your heart rate barriers should be, with resting, low, moderate and high heart rate thresholds added in.

For those familiar with traditional steps-based trackers, it’ll be strange at first, but once you get over the shock of being shown such low numbers, it quickly becomes a great motivational tool to get you pushing harder.

It’s recommended that you achieve 100 PAI a day in order to maintain peak fitness and prolong your time on this planet. Unlike 10,000 steps or 1,500 daily calories, however, that’s not an easy metric to meet.

You really have to exert yourself to get your heart rate in the point scoring intense active zone. We spent 45 minutes in a high intensity Combat Fit class quickly followed by a 22 minute 5K run and still only recorded 48 PAI points.

Yes, this makes it a great metric for the ultra-fit who are able to fit in a run, sport or heavy gym session every day, but it can also prove pretty demoralizing at times too. Spending a busy day walking between meetings in London we racked up more than 11KM of distance and more than 600 active calories burnt, but a grand total of 0 PAI.

That's because despite rushing around, we were never exerting ourselves enough to get our heart rate into the moderate or intense activity zones.

While some of this is down to the metric used and long-term exercise effort needed to meet this target, a bit of blame can also be heaped on the hardware itself, because although more accurate than many wrist-based trackers, the Slice’s inbuilt heart rate sensor isn’t without faults.

At rest levels, the Slice feels like it’s playing things safe, often erring on the side of caution with heart rate readings that are a little on the low side. Despite virtually every other wearable we’ve tested over the past couple of years telling us our resting heart rate is somewhere between 65 and 72bmp, the Slice regularly showed up a heart rate in the low 50s. That’s a big discrepancy when heart rate data is so key to this tracker’s abilities.

Get active and it’s reliably accurate, responding to minor fluctuations in your biometrics, but there are other issues.

The Slice is supposed to track your heart rate at 1 second intervals during exercise and every 5 minutes when your heart rate is below moderate activity. During testing this wasn’t always the case.

Running just under 1km to make a train, despite feeling out of breath, sweaty and being able to feel our increased heart rate, the Slice was still giving us a big fat zero on the PAI score. The heart rate sensor hadn’t kicked in during our period of increased effort.

Fortunately, it’s not just about PAI. Just because the steps count and calorie burn aren’t the focus of the Slice’s tracking abilities doesn’t mean they aren’t available, you just have to go digging for them. Once added to the device’s menu from within the app, you can find these with a few presses of the wearable’s single button.

Despite not being extravagant on the features front - there’s no inbuilt GPS or GLONASS skills here, the sensors that it does pack - including a 3-axis accelerometer - do a good job of accurately counting out your steps and calorie burn.

The Slice is more than just a fitness tracker too, as it offers message notifications and call alerts. These are pretty basic - there’s no reply or answer options - but being able to see the name of the sender scroll across the screen before the message symbol shows up is a handy addition.

Compatibility and app

  • App graphs out daily PAI earnings
  • Doesn't coach you to do more
  • Compatible with most iOS and Android devices

The Mio Slice might be like a dozen other fitness trackers when it comes to looks and its modest array of integrated sensors, but it's the custom companion app that can really make or break a device. Unfortunately, the Slice does little to push itself to the top of the pile here.

Open the app and you’re greeted with a circular chart pulling out your weekly PAI efforts on individual days. This looks great and is a brilliant way to see how active you’ve been, and, more importantly, how much effort you’ve put in.

Tap on any of these days and you’ll be offered a more detailed breakdown of your activity, including distances covered, steps taken and active calories burned. With the Slice also capable of keeping tabs on your sleep cycles, it will also show how much you’ve snoozed over the past 24 hours.

The main information here, however, is your heart rate chart. Showing how you earned your PAI points, it breaks down in intricate detail your heart rate at any point throughout the day, including the exact BPM and the activity range you were working in.

While it’s good to see how your body has reacted to certain exercise, that’s about it. The Mio PAI app looks good, but scratch beneath the surface, and things quickly fall short.

Instead of guidance on how to push forward with your fitness goals or increase your daily PAI score, you’re left on your own. There are no coaching elements here, no achievements or target points, and that’s disappointing.

A gadget that’s so geared to the more enthusiastic fitness fan needs to back up the data it captures with tangible benefits on the coaching and progression front. 

As it is, the Slice gets you excited to push your exercise efforts, only to leave you feeling hollow come the end.

It is widely supported though. Whether you’ve got an iPhone or Android handset, chances are the Slice will play nice with your smartphone, as it’s compatible with devices running iOS 9.0 and above and Android 5.0 and up.

Battery life

  • Up to five days of life on a single charge
  • Requires proprietary charging dock

Its app might disappoint, but the Mio Slice’s battery life doesn’t. Although Mio’s claims of a five-day battery life are slightly ambitious, we managed to get into a fourth day of use, with solid exercise sessions each day.

This staying power is aided by the lack of integrated GPS, but eaten into by the Slice’s heavy use of the optical heart rate sensor.

It’s par for the course when lined up next to the competition, matching the Fitbit Charge 2 when it comes to longevity, with the need for a couple of trips to the mains per week.

When it does come time for a power up, like so many wearable gadgets, the Slice requires a proprietary charger to give it a new lease of life. 

Its addition is somewhere in the middle of the convenient/awkward scale, requiring the wearable to be clipped in the correct way around and then placed somewhere spacious.

Annoyingly, although the Slice will alert you when you’re running low on juice, it won’t actually keep you informed on your remaining power until you’re into the red. At least not on the device. For that you’ll need to break your smartphone out and sync things up, a process that’s hardly ideal.

It might look like all the rest, but in a world of near carbon copy fitness trackers, the Mio Slice is trying something new. 

It’s a device designed to get you exerting yourself rather than merely walking, and does a good job of encouraging you to become fitter rather than just more active.

The PAI metric is key here and we really hope this sticks around and becomes a key component of other activity trackers, as it’s a great driving force to improve fitness. It needs backing up though, and that’s where the Slice ultimately fails.

What lets the Slice down most - besides a pretty boring look - is the lack of depth to its app. It shows detailed graphs of your heart rate range throughout the day, but doesn’t delve beyond and this stops it becoming a must-buy.

Who's this for?

The Mio Slice is for the fitness fan that wants to take their energy-sapping exercise to the next level and feel slightly smug that they’re doing things ‘properly’ in the process.

You’ll need to know what you’re doing in your fitness regime given the Slice’s limited app abilities, and a competitive streak would help as the PAI, although a more accurate gauge of growing fitness, could also be a serious motivation killer.

Should you buy it?

How fit do you want to be? The Mio Slice will push you to really up your high intensity exercise levels, but can be quite demoralizing if you’re simply looking to become more active and burn a couple more casual calories.

It’s affordable without ever really being cheap and its look isn’t going to inspire. It’s a solid effort, but not one that’s done enough to edge the Fitbit Charge 2 out of fitness tracker top spot.

First reviewed: February 2017

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