An Update on the Mio SLICE: How to get your slice of PAI


When Ray asked what readers wanted to see from CES this year, several of you commented about the Mio SLICE and the current status of its availability.  I had the chance to sit down with the folks at Mio and talk through where they are with SLICE and what the next few months look like.


You may remember that Randy covered the announcement of the SLICE last year at CES as well as the beginning of their pivot away from a 10,000 step goal for activity tracking.

The 30-second version of that story is that 10,000 steps simply isn’t a satisfactory metric for all people.  A balanced activity profile will include strength training, cardio, and some amount of stretching/yoga, and an activity tracker counting steps is only likely to capture part of that story.  For example, if you are into paddle sports and spent 90 minutes in a kayak, the resulting step count is likely to be lower than you would expect for your activity output.  That is simply the truth of counting steps (as anyone who has ridden 5 hours on a bike knows, only to have their watch beep upon saving the activity to ‘Move’ that hour).

Now let’s be clear, there is nothing inherently wrong with steps, Mio is just taking a slightly different approach in their aim to track a more holistic look at activity through heart rate.  Enter the Personal Activity Intelligence, or PAI (pronounced PIE).  Mio is pulling from the Hunt study and combining the work done there with their own algorithm to associate a given cardiac output (heart rate) over time with a score they call PAI.  This is where it can get a bit ‘interesting’.

Rather than a daily PAI goal, they monitor a rolling 7-day value.  Mio has set the target at 100 PAI (it sounds a bit arbitrary, but it’s a round number, and who doesn’t like round numbers?).  They then take your information (age, gender, resting and max heart rate) and use that to measure the quality and intensity of your cardio workout.  Kayaking for 90 minutes will likely result in more PAI than a walk after dinner (unless your walk turns into more of a Forrest Gump style cross country journey).

The other piece of the puzzle is not all PAI is created equal.  If you aren’t in the best of shape now (as calculated by the correlation of age/gender/max and min HR) you can earn PAI easier than someone who is in marathon shape.  In that same vein, if you are a committed cross fitter, you might be surprised by the lack of PAI earned for a workout, especially as you get faster at the workouts. Mio is squarely targeting activity tracking by heart rate here and PAI is simply their method of quantifying ‘active minutes’.  If you’ve had a few good days in a row and are well over your 100 PAI mark, today may be the day for Yoga or something less intense than interval training.


So with all of that said, is the product finally – a year later) – shipping?

Yes. Or, mostly.

The Mio SLICE is available for purchase now, but only exclusively through Brookstone as the official launch partner (For those outside the US: They sell gizmos and gadgets you never knew you needed until you spend an hour in their store watching metallic balls bounce magically in the air).

There have been some reports that supply has been limited but Mio expects to have plenty of inventory when they begin selling the device on their website and through other distribution channels.  For those of you who don’t live near a Brookstone, they anticipate having units available elsewhere starting in February (I imagine the exclusivity deal runs out January 31).

Most notably, this is timed nicely as Mio is continuing development for the platform and will be releasing updates over the coming weeks to continue ensuring that the product meets their standard for quality and accuracy.  Said differently: They’re still working out some kinks – but they expect those to be sorted by February.

DSC_9600 DSC_9601

Given Ray is off to Australia for a few weeks, it won’t be until after then that he’s going to dive into it.  But, as you can see by the two pics above – he does indeed now have a unit, and it even made it to the famed unboxing table.  He is planning on spending some time with the SLICE when he gets back and will have more to say around accuracy, PAI, and the general pivot away from a pure steps metric.  Stay tuned for that sometime in February!

Catch all the CES 2017 posts here in one handy to read page.  And fear not – there’s still a bit more to drag out of the CES product pile that somehow nobody else talked about yet.  So stay tuned!


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  1. Colin

    I hope this works like the older Mio Fuse and transmits HR data to my Garmin for cycling. I’d love to replace the Fuse with something less bulky.

  2. It’s available to buy on their website now: link to
    Can’t figure out yet if it re-broadcasts or not.

    • nasser

      from Mio SLICE Manual:
      – Mio SLICE can stream your heart rate to any fitness apps and devices that support Bluetooth or ANT+ heart rate streaming. For best results, put SLICE into Workout Mode and ensure your phone remains nearby to stay connected.

  3. morey

    Nice. but what we really want isn’t another fitness tracker (although I applaud Mio for their direction with this one), but an optical wrist based HR monitor with a longer battery life, better accuracy and HRV. If Garmin can make a watch that has a HR monitor which lasts 15+ hours, there’s really no reason why Mio can’t.

  4. Ben

    Silly question, but does this thing display the time and date? You can’t really tell from the marketing shots, as they are so focused on PAI.

  5. gl00

    you refer to kayaking a few times… if there’s one sport that works bad with optical HR sensors, that’s kayaking (way too much wrist movement, forearm tension, strong and fast HR variations, cyclic movement…). So far I still have to find a wrist based optical sensor that would work for kayaking…

    in case MIO themselves made references to Kayaking, that could be a very interesting detail… but I guess you chose this example merely by chance?

    • Shane Porteous

      Have you tried the Scoshe Rhythm +?

      My wife has used that for the last 2years with very little issues.

    • gl00

      nah… they’re quite difficult find in this part of the world, plus I’m more interested in wrist based sensors I can wear all day like a watch, out of convenience…

      for now I use Tshirts with integrated HR straps that are comfy and accurate enough when my watches’ OHR won’t work… only issue being that it limits what I can wear… :p

      thanks for the tip nevertheless!

  6. Tom Albrecht

    “spend an hour in their story” Should be ‘store’.

  7. Falko

    What kind of HR sensor do they utilize?

  8. James

    Whoop seems to be much better measuring HR 100 times a second, but it is much more expensive. Hopefully, we will soon see review of Whoop from DC Rainmaker soon 🙂

  9. tfk

    I loved the MIO Link (and related models). They still stand up to the competition in 2017, IMO.

    I saw one of the early mock ups of the slice in March 2016 and a MIO presentation. The looks seem to be much improved. I kinda like it.

    It’s great that it broadcasts HR (see comments above)

    PAI seems to be doing something a bit cleverer than steps. That’s great. There must be SOME benefit to that.

    *BUT* I’m not sure how or why it is anything new

    For example is it looking at HRzone/durations and assigning a score? If so, that was done with TRIMP in the 1960s.

    Maybe it is assigning ‘points’ for movement. Fair enough, that’s giving some credit at levels that TRIMP won’t really cover.

    But is it really any different or new to Garmin’s INTENSITY MINUTES?

    @James mentioned WHOOP. WHOOP, on the face of it, seems a whole lot cleverer (and more expensive) allowing both the manual entry of RPE (there IS a good basis for assigning TRIMP-based on RPE in team sports). WHOOP also CLAIM to be doing HRV on the wrist with their in-house developed sensor (so I was told)

    So the SLICE seems perfectly fine on the face of it. But “very 2015” in the tech.

    I’m sure I’ve missed something.

    • Mike Richie

      Must say, I’m not sure how helpful intensity minutes are. My normal week has them at about 10x the goal (1500 minutes) and I am, by no means, a major (or any kind of) athlete. My current minutes are at 941 and it is only Thursday. The doubling of minutes for intense activity means my weekly goal can be met in one workout (and then I usually ride a bike more than I drive). Kind of a useless stat. Points that can be somehow tailored might be more useful.

    • tfk

      TRIMP is HR zone-based and hence s/be personalised.
      not sure of the exact calc of intensity minutes (IM)…if you are an athlete I reckon IM probably of no use

  10. DT

    I hate to say it but I returned mine. Kept on dropping connection and it had me walking 38 miles a day when I only walked 3. My PAI on the band was different than the app. I do know they are constantly updating the firmware. I will try again in a few months.

  11. Josh

    I returned mine. I found it wildly inaccurate, had consistent drop issues, and the battery life was a meager 2 days (while not working out even). There were other things that bugged me about it too — no alarms was a biggie. Plus it gave me a pretty awful rash in just a couple days.

    1 year later…they definitely could have done better.

  12. Alan

    The PAI is very interesting. I have suggested that Mio may be even more successful with this metric if they have an Apple Watch app that would track PAI. There are already millions that have this hardware. So the installed base already exists that may be interested, like me! But I don’t necessarily want to wear their band. I emailed one of their researchers and PAI scientists and was told this would be released soon after the Slice. I would definitely buy this type of app.

  13. Alan

    Also big question is accuracy of optical HRM.

  14. I found this blog very interesting. I will tell all my friends about it

  15. Ingo

    So they basically came up with their own training load methodology and put it around people’s wrists? Hardly ‘wow’ given that TRIMP (including TSS, ATL and CTL) is an almost 25 year old concept…

  16. Justin

    Hi all,

    Anybody tried it while swimming? Is it reliable?


  17. Zeke

    I’m very keen to see a DC Rainmaker review of the Mio Slice, especially in terms of HR accuracy in comparison to Garmin’s Vivosmart.

    Any sneak peaks, teasers or ETAs on that front?

  18. I look forward to seeing the in depth review. Especially heart rate accuracy.

  19. jamey ward

    Is there going to be a review on this product? just wondering since this has been on the blog for a bit????
    Hopefully soon?

  20. Brandon

    Any updates on getting an in-depth review?

  21. Nox

    Waiting hopefully for a full review. I’m really on the fence with this one and your tests are always great.

  22. NR

    There are lot of contradictory reviews about Mio Slice (regarding battery life, accuracy of data, comfort of use etc). Before deciding, awaiting your take on this because your analysis are always spot on. Thanks.

  23. SS76

    Until Mio does something with their APP which has to be amongst the worst, they will never get my money. Also, not sure how accurate the Optical HR sensor is since they are no longer using the phillips one they had previously. Funny how PAI is totally dependant on the HR readings, what if they are not accurate? Big questions here.

  24. Zeke

    I ended up buying a Slice.

    Yes, most of the known issues from other reviews/comments have proven true, no surprise there: very slim app functionality; poor battery life (2 days); very bad legibility in direct sun light; etc.

    But the features that enticed me to give it a go anyway, have also proven true: HR broadcasting over bluetooth (its been solid with my iPhone); 24/7 HR and sleep monitoring; and a simple activity tracking metric, not counting steps, that will motivate this aging-used-to-be-fit-now-tired-dad to get off the couch.

    I can’t speak for accuracy (that’s where Ray’s going to comes in :), which of course directly affects those last two features that I like. The whole premise of Mio’s PAI after all, is heart rate. Though, I have done some crude validation on HR results I’m getting, and so far it seems close enough for my “couch to 5k” needs.

    There are two significant issues though, that I think anyone interested should know. First, the app only tracks 7 days of activity/data. And that’s not just for your PAI score either (for which 7 days is the point), but for all historical data. There’s simply no way to review your HR, sleep or activities beyond 7 days. In my case, all I’m left with is HR data for activities I’ve recorded in Strava. Second, the iPhone PAI app won’t open if it fails to sync with Mio’s servers, and this happens to me multiple times a day. Why can’t it just open, and attempt another sync later? I don’t know. Ridiculous.

    Anyhow, overall I’m happy enough, but I wouldn’t recommend it until some of the app issues are sorted.

    • Thanks for taking the time to post, I appreciate it. Accuracy is definitely HUGE. Fortunately their past device (the link) was good enough outside cycling (which was the only thing I was trying to use it for so I returned it). The 2 days battery life is atrocious. And only keeping data for 7 data is mind boggling. So glad I haven’t bought one. Mio also told me they currently don’t have a move reminder. A HUGE miss IMHO.

  25. JohnPaul Agius

    Zeke, that 7 days tracking is one of the issues I have. No historical data to bench mark yourself against and see progress over time. Mio has been told this many times. I’d say this issue, along with no integration with MyFitnessPal, and connectivity issues are the big ones.

  26. DOug

    Had Slice for a week. Returning it. Heart rate accuracy is very bad. I bought it because it has ant+ which means no hear chest strap while biking and links to my bike computer and bike computer records. Any other features would be bonus. Unfortunately, heart rate accuracy is VERY BAD!!. In the middle of a high intensity ride where I know I’m in the 160+ range, slice has me at 109. No matter what I do (based on MIO troubleshooting advice – move to different wrist, move it higher up, clean the contacts) it just failed to give me accuracy. Too bad.

    • Thanks for posting. Appreciate it. It’s pretty much as I was figuring based on my experience with the Link. Mio even tried to convince me it was an issue the the one I had … the next one was just as bad link to Cycling + wrist = bad IMHO and mountain biking makes it even worse. Look at what Ray said about even the latest Garmin Vivo Smart 3 Wrt to cycling “In case it’s not overwhelmingly obvious above (the yellow line): It sucked.  Badly.”

  27. Josh

    It’s unanimous. It’s a turd…I wanted it to not be, but it is…

  28. Patrick QC

    I’ve been using it daily for 10 weeks. It’s my first and only wearable since my old Polar chest strap, so I can’t compare with any competing product.

    As others have said, there are some issues: impossible to read under the sun, especially with sunglasses; very limited app functionalities; poor battery life (2 days, sometimes 3 if I had a rest day), but it does charge very quickly. These issues are not a problem for me, but if they are for you, you’re warned.

    The major issue for me is lack of historical data; you can only see the data for the lasts 7 days. Like I presume several others using these devices, I’m a bit of fitness data nerd, and it really frustrates me that I can’t analyse patterns in my training, and PAI distribution. I don’t get why they don’t offer a website where we could see our data, or at least provide us with a way to export to excel.

    There were also a lot of syncing issues with the app in the first few weeks, but no problem in the last 4-5 weeks.

    Accuracy: it seems very accurate to me. I mostly do weightlifting; for cardio, I use a rower, I run, I power walk with a weight vest, and I do metcons (similar to Crossfit). I use my bike only for commute at a slow pace, so I can’t really comment on accuracy issues while biking.

    Sleeping: I’m amaze how precise the sleep analysis is, and I already discovered a few patterns (but again, lack of historical data!)

    I decided to buy the Slice to have more motivation to do cardio, and to better understand the impact of my training. I really like the PAI system, it adds a game/challenge to my training, and I’m trying different workouts and intervals. I made several changes to my cardio training based on PAI results, and I’m seeing the benefits.

    So, in a nutshell, I’m happy with my purchase, but frustrated by the lack of historical data and analysis tools.

  29. alibi

    even without study backing pai have some logic behind.
    but “dumb” activity tracker is not very interesting now. hope mio remember they connections with garmin and will make metrics available on fenix\etc..

  30. Aydin

    Hi Ray, I came across a study about wrist-worn hr monitors the other day and was wondering if you have seen it and what is your take on this?

    link to


  31. erkelbot

    And the lights of Mio’s eyes dim…Goodnight sweet prince. Too bad you couldn’t get it right… RIP.


    We’d like to update you about some big changes taking place at Mio!

    Over the years, we’ve built a reputation for innovation in fitness wearables and accurate heart rate monitoring. What drives us forward is our continuous mission to improve people’s health and fitness through easy-to-use wearable technology providing meaningful biometric insights.

    As you may know, our latest innovation is PAI (Personal Activity Intelligence) – the new activity tracking metric and app. PAI was first introduced on the Mio SLICE earlier this year. Moving forward, in order to accelerate the adoption of PAI, we are working with partners who have successfully scaled and are looking to grow further with innovations in sensor analytics.

    As such, we have made the decision to no longer produce devices ourselves, and we are instead working on developing a cloud-based software platform that will integrate with other devices and systems to expand the PAI ecosystem. We sincerely thank you for your patronage and loyalty over the years, and we want to assure you that we will continue to handle your support inquiries related to any Mio products purchased.

    One of the exciting projects we are working on is developing a PAI Apple Watch app which will be available early 2018. This will allow many new people to benefit from using PAI.

    To align with our new focus, we will be changing our brand name from Mio Global toPAI Health. Our new website is and our social media is changing to PAIhealth as well.

    Our vision is to optimize anyone’s path to being healthier.
    We hope that you will continue to follow us on our journey. We are excited about our next chapter, as we work to positively impact global health through PAI.


    Peter Taylor
    CEO, Mio Global / PAI Health

    • Jamey Ward

      Yep it’s sad. Ironically they are stopping producing devices(which they did decently) and focusing on Apps and software to leverage to others.(which up to this point was their Achilles heel) Maybe this will allow them to get better at it. I hope.

    • John Galea

      I’ve not had a good experience with their devices so not much of a loss. As for PAI I’m not sure I care about that either so all in all, life goes on.

    • PAI was like Garmin Intensity Minutes or like HR-based TRIMP. A couple of years ago I asked someone from MIO doing a conference presentation on PAI to explain the difference and they had no idea. (luckily I asked them afterwards in private as i suspected the answer I got woudl be what it was). It’s a good idea…just not a new one. (Bannister et al 1960-something???)

      I think Liz D stood down in some form a couple of months back and I also thought their decision to focus on apps/software was announced quite a while back too. Could be wrong.

      A HR-basesd TRIMP app might be an idea if the optical HR tech is accurate. IF not it will lead to absoute rubbish interpretations (I’ve used TRIMP for YEARS…not optical HR based TRIMP)

      MIO Link – ah those were the days. Great product.

    • Mark

      Hi the5krunner,
      You tested the Mio Slice which has memory with a Fenix 3 or 5 in a pool swim and does it upload the HR data post the swim, similar to Garmins HRM-Swim chest strap ?

  33. sS76

    This has been coming for a long time, I had contacted them many times with respect to the poor app and how they render their devices useless. Well I guess I was proven right. RIP Mio.