Mio Slice with PAI – Built for Smartphones?

At a Glance: Quick Ratings

Heart Rate Functions


Fitness / Sport Features


Ease of Use


Battery Life


Where To Get It

A Deep Dive Into Mio Slice

The Mio Slice is the world’s first activity tracker to feature PAI. Personal Activity Intelligence is a measure of heart rate intensity throughout the day. Mio realised that counting steps is not necessarily the most effective method of measuring personal activity throughout the day. The Mio Slice has been reviewed by Tristan Haskins.

  • Who Is It For?

  • Video Review

  • Pros

  • Cons

It took me a few days to fully appreciate the Mio Slice and PAI(¹). I have spent many hours testing fitness trackers with a daily step target, generally aiming for a 10,000 step daily target. The Mio Slice promotes a very different and innovative activity goal. The Slice utilizes the PAI system of activity tracking. PAI stands for Personal Activity Intelligence. In summary it’s an algorithm based on heart rate intensity and duration rather than just steps. The aim is to achieve a 7 day rolling total of 100 PAI or more. The Mio Slice measures heart rate continuously throughout the day to provide the PAI score.

NOTE > you must have a smartphone to setup and manage the Mio Slice. It is NOT possible to use it in a standalone state. Do not buy the Slice if you don’t own a smartphone (iOs or Android).

Aim for 100 PAI per week
The aim is to maintain a running weekly total of 100 PAI. In the two weeks I have been using the Mio Slice I have seen between 114 PAI, my lowest 7 day score, and 125 PAI, my highest. The Mio Slice is for those interested in effectively monitoring their daily activity /intensity, BEYOND step counting.

How PAI Works

PAI is a solid, scientifically supported method of measuring daily activity intensity analysing 24/7 heart rate as well as steps/movement. The aim of PAI is to achieve a 7 day rolling total of 100 PAI. Your Personal Activity Intelligence score is precisely that, it is tailored to you and your current fitness level. The level of activity required to achieve a PAI score of 100 is different from one person to the next.

An unfit person with no history of exercise will need to do a lot less physical activity than a professional athlete to achieve a PAI of 100. I had to run three times per week and cycle once to achieve a PAI of 0ver 130. That’s 5 hours of exercise spent in and around 70% of my maximum heart rate. More about the science behind PAI here.

Does it Work?

Yes. In my honest opinion PAI is far better for monitoring and assessing your daily activity than steps and distance alone. It’s hard work to achieve a 7 day rolling PAI of 100, but that challenge makes it motivational. There’s no point setting a goal that is too easily achieved. PAI is personally set just for you. It also adapts as you get fitter. If you start regularly exceeding your 100 weekly rolling PAI score, the Mio Slice and PAI app will make it just a little bit harder to achieve next time. This increase in target intensity will help get you fitter over time.

Just ONE Goal … 100 PAI

The beauty of the PAI system is the simplicity. Maintain a PAI score of 100 and you’re on the track to improved fitness and well-being. The Mio algorithm may make it harder (or easier) for you to achieve the magic 100 PAI score, but that doesn’t concern you. Simply aim for a PAI of 100 and everything will fall in to place … easy.

Expect to see PAI adopted

I would not be surprised if we were to see other key players in the fitness tracking sector adopt PAI in the next few months. I am quite confident Garmin could add it as a WIDGET to products like to Vivosmart HR, Vivoactive and Forerunner 235.

The following images were taken during the installation of the PAI app.

Main Features and Functions

  • Mio Heart Rate Technology – the original innovators of WRIST BASED heart rate
  • All Day Heart Rate Tracking – the Slice records your heart rate 24/7
  • Personal Activity Intelligence – Aim for a PAI score of 100 points per day
  • Activity Tracking – tracks steps / distance / calories burned
  • Broadcast Heart Rate to other ANT+ devices, eg Garmin Edge
  • Water Resistant – Up to 30m / 100ft (fine for surface swimming)
  • Sleep Tracking – monitors the quality and duration of your sleep
  • Smartphone Notifications – receive smartphone alerts for calls, texts etc
  • Watch my Video Review
  • Review conclusion
  • Check best prices

Real-world Battery Life

Mio quote a battery life expectancy of “Up to 5 days (depending on usage and settings)” In practical use training for 1 hour per day I got 3 full days out of the slice. That is with regular APP connection, smartphone notifications turned on and, importantly, BROADCASTING the heart rate via ANT+ to my Garmin. With broadcast turned OFF the battery life expectancy extended to 4 full days including 4 hours of moderate to high intensity training. (PS … adding a LOW BATT alert to the watch unit would be a nice feature rather than having to rely on checking the battery charge status in the APP)

Wrist based Heart Rate

The images below show the rear of the Mio Slice and it’s patented LED sensors. These sensors read the heart rate directly from your wrist 24/7. This is how the Slice can calculate a PAI score. Mio were the innovators of this strapless heart rate monitoring and can be thanked for releasing us from the need to use a chest strap. Please read on for details on the Mio Slice’s heart rate accuracy.

Slice HR Sampling Rate

The Slice samples heart rate every 1 second when in exercise mode or during high intensity activity throughout the day. During low to moderate heart rate throughout the day it samples every 5 minutes. When sleeping the Mio Slice takes a heart rate sample every 15 minutes.

More Features

Mio Slice Heart Rate Accuracy

Broadcast Heart Rate (ANT+)

Additional Review

Mio Slice showing daily steps so far. The Slice focuses on the PAI weekly rolling activity total of 100 or more, however, it can still be used like a traditional fitness tracker with daily step counting.

The Slice also shows calories burnt indication. These calories are IN ADDITION to the calories your body burns throughout the day (basal metabolic calories) The calories shown are those burnt during activity and exercise.

Like most other fitness trackers the Mio Slice also monitors sleep duration and quality. A more detailed assessment of your sleeping patterns can be found in the PAI app.

An Insight in to My First Two Weeks

The screen-grab below was taken from the Mio PAI app midway through my second week of testing the Slice. A large portion of my weekly PAI score of 110 is from Sunday. This was a 20 mile bike ride (Strava details) with an average HR of 146bpm and a maxHR of 171bpm. It was a reasonably hard ride with a strong headwind on the way home. Stave awarded it a SUFFER SCORE of 51. The Mio Slice awarded a PAI score of 64. As I suggested earlier, for those familiar with Strava’s SUFFER score, PAI is similar. It’s a different algorithm and they figures are NOT directly comparable.

The image below is a screen-grab of the heart rate data from that same bike ride. The PAI app splits the session in to zones of LOW, MEDIUM and HIGH intensity. Most of my PAI score (31 points) came from the time spent in the HIGH heart rate zone.

Devices Settings via the APP

The images below give an insight in to the level of settings that can be adjusted on the Mio Slice. Everything from smartphone notifications to screen brightness, wrist gestures and ANT+ heart rate broadcast can be set here.

You can even select what parameters are shown on the Slice’s display. I have chosen everything giving me access to Time, PAI, PAI today, Heart Rate, Steps, Calories, Distance and Sleep. I would like to have seen DATE as well? something I have asked the team at MioGlobal.

Questions sent to Mio following Review

Here are some questions I sent to MioGlobal following my review of the Slice. Their replies are in BLUE

APP history. I have been using the Slice for nearly 2 weeks but I can only scroll back in the history to the last 7 days … I appreciate that PAI is a rolling score of daily activity for the last WEEK, however, it would be great to have a MONTHY summary view showing the weekly PAI achieved last week, 4 weeks ago, 3 months ago etc… Or maybe I am missing a feature in the APP?
>> We have a trend and history tab currently in development. This will be released in the next major release.

The Strap … I really wish all fitness band designers would go for a traditional BUCKLE and PIN … the Mio Fuse was spot on. I personally don’t get on with the system on the Slice at all. Maybe it’s just me, but give me a “normal” strap any day … or look a the TomTom Spark 3, that’s different but easy to use and adjust.
>> We will certainly take this onboard when looking at future models.

No Date? I assume it would be easy add a DATE option screen to the app as you have distance, steps etc.
>> A date could be possible and this is something we will assess with our design team.

No Alarm? Making use of the vibrate function for a silent alarm would be useful
>> An alarm function is in the next major release.

Broadcast – is it possible to extend the HR broadcast to Bluetooth as well as ANT+ ?
>> MY ERROR … Currently Heart Rate is broadcast via Bluetooth and ANT+. ANT+ is limited to broadcast in workout mode only (when a user records an activity) Bluetooth is what we use to broadcast Heart Rate as default. This works for all day mode and workout mode.

Display ALWAYS ON option when in training mode … something I’d really like to have when doing interval training (running) as I like to push to 160bpm then back off … wrist gestures are fine, but option for permanent on would be useful
>> Interesting idea, the main issue that occurs here is the amount of battery required in order to keep the screen on. What we do have in workout mode is for the last screen to always show when the screen does turn on. This way in you example you mention the HR screen will always show unless you want to toggle to a different screen.

MANUAL ADD. If I forget to charge my SLICE and have to leave it charging in the morning when I go for a 5 mile run, I’d like the option of a MANUAL ADD PAI e.g. Add a PAI of 20 for my 5 mile run.
>> MY ERROR … This is a current feature. On the day detail page go to ‘Activities’, there you see the blue plus with a circle  This allows you too manually add an activity. You need to input duration and how intense your activity was. This will calculate PAI points for you and them to your PAI score.

With this is mind having a PAI SCORE calculator APP would be great. Some way of getting a close to precise PAI score just by entering my age, sex, weight, resting HR, maxHR and AVERAGE HR over a period of time eg. Make, 48yrs, 75kg,

Resting 50, MaxHR 180, Average HR 150 over 45 mins … PAI equivalent = 22 or similar. This would be useful not only for 7 (manual add) but also for understanding what I may need to do to achieve my weekly 100 PAI score.
>> We are discussing a more integrate PAI calculator like the situation you are describing that will allow users estimate what they can earn for different scenarios.

Does achieving a weekly PAI of 100 get progressively harder to achieve as I get fitter? In other words, is the bar raised to make it more challenging or will I just keep over achieving and getting a higher PAI score. In other words. Right now I have achieved PAI scores of 140 and 165 …. Will the system “learn” t,/hat and make adjustments in a similar way to Gamin Connect adjusts your daily step goal based on your training / activity pattern … sorry if this doesn’t make sense, just trying to fully understand it
>> The higher your PAI score, the harder it is to earn PAI points. For example, today you went for a run and earned 40 PAI points, the very next day you did the exact same run, same distance and intensity. You will not earn 40 PAI points, you will earn less.
When you reach a higher PAI score it’s more difficult to earn PAI points and maintain that score, so you will need to work harder to earn PAI points. Over the 7 day rolling window, it’s more work to stay at 100 or above than it is compared to reaching 100.

Review Summary

If I am totally honest, I was skeptical at first. However, having used the Mio Slice for a couple of weeks now I am totally on board.

Anyone bored of achieving their daily step count with little effort looking for something more challenging, consider the Mio Slice. Anyone who achieves their daily step target but doesn’t see any obvious improvement in their physical fitness .. again, consider changing to a Mio Slice.

The introduction of PAI to a fitness tracker is a ground breaking innovation. It may be precisely what we need to motivate the general public to a healthier lifestyle. It’s no surprise to me that it has come from the company that brought us strapless heart rate monitoring. The Mio Slice is one of the best fitness trackers of 2021 – Thanks Mio – GREAT JOB!!

Andrew Wyatt

Andrew Wyatt

Andrew Wyatt has been a tech geek for as long as he can remember. Whether it's laptops, cameras, or projects, he's obsessed with it all. When he's not researching the latest tech products, he likes to go on long hikes with his dogs.

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