Review: Mio SLICE, make sense of your personal heart rate data

Mio Slice




Ease of use


Use of information





  • Simplifies fitness tracking
  • Uses scientifically validated metric
  • Accurate heart rate measurements
  • Water resistance


  • Screen visibility poor in daylight
  • Bland design
  • App would benefit from more features


Vancouver-based Mio Global has recently launched its new fitness tracker called Mio SLICE.

The device, which was originally announced at last year’s CES, is now available for purchase. In an increasingly competitive market, Mio Global is trying to stand out from the crowd by replacing step count with a brand new health metric. Called PAI, it provides you with a personalised target score which reflects your body’s response to physical activity based on heart rate.

Essential readingTop fitness trackers and health gadgets

The company says studies show that keeping your PAI score consistently above 100 will increase your lifespan by up to 10 years and provide maximum protection from lifestyle diseases. SLICE is the only Mio product to display the PAI score directly on the band itself. Owners of its other products are, however, able to view scores on the PAI mobile app.

I’ve had SLICE strapped on to my wrist for the past few weeks. These are my impressions.



Out of the box, SLICE looks like most standard fitness trackers. It sports a TPU strap, anodized aluminum main body and snap-on buckle. The device actually comes across as a blend of the Fitbit Charge 2 and Garmin Vivosmart HR. While it will probably not win any design awards, SLICE is quite distinct from all other trackers in the Mio range.

Review: Mio SLICE, make sense of your personal heart rate data

There are two sizes to choose from. One for small wrists measuring 5.5” to 6.75” / 13.97 cm to 17.15 cm in circumference – and another one for larger wrists measuring 6.75” to 8.25” / 17.15 cm to 20.96 cm in circumference. There are also a number of colours to choose from including Black, Navy, Stone and Sienna.

Measuring only 29 grams, this is a very lightweight fitness tracker. In fact its so light, once its on your wrist you’ll probably forget that its there.

The OLED display is by default off, but it springs to life as soon as you lift your wrist. The large fonts are very clear and easy to read indoors. Unfortunately, the visibility of the screen deteriorates rapidly once you step outside the front door. Even tweaking the visibility setting to high does not sort the problem.

Review: Mio SLICE, make sense of your personal heart rate data

All your metrics can be seen on the device itself. You scroll through the individual screens (time, PAI, PAI today, heart rate, steps, calories, distance, sleep), by repeatedly pressing the single physical button on the tracker. This screens can all be tweaked and customised as per your liking.

Under the hood are the optical heart rate tracker, 3-axis accelerometer and vibration motor. Most important on this list is the optical heart rate sensor as this is what is used to calculate your PAI score. You can connect SLICE to other devices, as it is capable of broadcasting heart rate data via both ANT+ and Bluetooth Low Energy.

Review: Mio SLICE, make sense of your personal heart rate data

Mio Global says you can squeeze approximately 5 days of battery life out of the tracker, with 1 hour of high activity time per day. In my experience this is a bit optimistic. Up to 4 days is perhaps a more accurate estimate. Which is still okay, but a few more days would have been nice. I am guessing because the tracker measures your heart rate often, this puts a strain on the battery.

On the plus side, an hour is all it takes to charge it from zero to full. Charging is done via a proprietary charger which plugs into any standard USB port.

You can keep SLICE on 24/7 thanks to its 3ATM water-resistance rating. This means its safe to shower or bath with it on, or even go for a swim or dive down to 3 metres depth.


In terms of fitness activity, SLICE tracks metrics that we are pretty much accustomed to seeing such as steps, calories burned, distance, all day heart rate, resting heart rate and sleep. It will also dish out smartphone notifications and provide vibrating alarms when needed.

This is where all similarity between Mio and other activity trackers ends. It now gets more interesting.

Review: Mio SLICE, make sense of your personal heart rate data

According to Mio, this tracker does something special which will help you live longer and reduce your risk of lifestyle-related diseases. Instead of focusing on the “10,000 steps” rule which has been adopted by most wearables manufactures, Mio has introduced its very own Personal Activity Intelligence (PAI) index.

Essential reading: Mio Range of Activity Trackers

The PAI algorithm is based on the HUNT Study, one of the largest health studies ever conducted in history, in which more than 60,000 individuals were closely monitored over 20 years. The HUNT study links activity levels to health outcomes. Apparently, keeping your PAI score above 100 will increase your lifespan by up to 10 years and provide maximum protection from lifestyle diseases.

Review: Mio SLICE, make sense of your personal heart rate dataUsers are told to aim for a PAI score of at least 100, which is calculated over a seven-day period. The quantity and intensity of activity required to achieve that goal is personalized based on a user’s profile, such as age and gender.

Essential reading: Should you really aim for 10,000 steps per day?

I have no problems logging 10,000 steps per day, and on most days I am comfortably above this number. What came as a surprise to me was that simply walking around would not bump up my PAI score very much. You really need to break a sweat and go occasionally for a jog or a run to get your heart racing and PAI score climbing.

As mentioned, you can view all your stats on the tracker display by scrolling through the individual screens. For more detailed stats, you will need head over to the smartphone app. To record an exercise session such as a run, long-press the physical button on the tracker and do the same once again when you are done.

This tracker is all about simplicity, and the app is no different. The home screen shows a rolling weekly pie chart of your PAI score. All it takes is one glance, and you can immediately see where you are and how much more work you need to put in to edge your PAI score above the magic 100 figure.

Review: Mio SLICE, make sense of your personal heart rate data

In essence, the PAI score loosely mirrors the general recommendation that you should put in 30 minutes of moderate exercise five days per week. But it is more individualised because its calculations are based on your personal profile. A good rule is that one minute of vigorous activity provides the same health benefits as two minutes of moderate activity.

The app also shows you a live reading of your heart rate, along with your resting heart rate. My resting heart rate was perhaps a bit on the low side, but these metrics vary from device to device. As long as you are using the same wearable, you are comparing like with like. The same was the case for my step count which I found consistently below the Garmin Vivoactive HR I was wearing on my other wrist.

Review: Mio SLICE, make sense of your personal heart rate data

The Day Detail screen charts your heart rate from the past 24 hours and breaks this down into Low, Moderate and High readings (a simplified version of heart rate zones). It also shows your distance, active calories, steps and sleep stats (Deep, Light, Awake time).

Review: Mio SLICE, make sense of your personal heart rate data

What is missing is a historical overview of your activity. I would have liked to have seen a chart showing how my PAI score, step count and other metrics change over time. You can go back seven days by clicking on the individual days in the pie chart, but this will only provide you with a 24 hour overview for that day. Lets hope Mio Global rectifies this soon with a software update.



One individual’s path to fitness may be very different from another’s, which emphasizes the need for a personalized approach to monitoring health and fitness. Mio devices are well known for the accuracy of their heart rate measurements. The company has now taken what it does well and come up with a novel way of measuring physical activity.

Now I can’t vouch for the science behind the PAI metric as I have not worn it for 20 years, but it is validated by one of the largest health studies ever conducted in history. And more importantly, it does make sense as it loosely corresponds with the recommendation that you should put in 150 minutes of physical activity per week.

Review: Mio SLICE, make sense of your personal heart rate data
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Review: Mio SLICE, make sense of your personal heart rate data

While by no means perfect, those looking for a no-hassle fitness tracker will be happy. If, however, you are looking for something more comprehensive and like to sift through detailed stats, you may want to look elsewhere.

SLICE does the basics well and provides you with a simplified metric which will let you know at a glance whether you are active enough. With so little to distinguish fitness trackers these days, it is a breath of fresh air to see someone take a totally new approach to keeping people fit and healthy.

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Marko Maslakovic

Marko founded Gadgets & Wearables in 2014, having worked for more than 15 years in the City of London’s financial district. Since then, he has led the company’s charge to become a leading information source on health and fitness gadgets and wearables.

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