the Nix Hydration Review – Garmin & Apple Electrolyte sport biosensor

nix hydration review biosensor patch sensor top and bottomNix Hydration Review

This is a review of the Nix hydration sensor, which is worn on the biceps and monitors electrolyte loss to track hydration levels. The sensor provides unique insights, but I found it to be too expensive and difficult to use on a regular basis. I would prefer a cheaper and easier-to-use product that integrates well with the tech platforms I already use, notably Apple or Garmin watches. However, Nix does support these platforms, but not in the way I would prefer.

Price when reviewed: NixBiosensors $129 (£109) includes 4 patch refills, normally $25 (£22).

Verdict: ⭐⭐⭐ - Good! and surprisinlgy useful. Let down only by the price and Garmin integration.
  • Price
  • Apparent Accuracy
  • Build Quality & Design
  • Features, Including App
  • Openness & Compatability

Summary: Nix Hydration Biosensor Review

Nix Hydration Review Summary

I recently tried out the Nix hydration sensor and overall, I found it to be a useful tool for tracking my hydration levels during my workouts and races. The sensor is easy to use – simply clip it on, start the phone app and watch app, and begin your workout. After a few minutes, the Nix biosensor will start providing live feedback on how much I’m sweating and how salty that sweat is. This information is crucial for knowing how to properly rehydrate, especially during hot summer races or training sessions.

Before starting my workout, I can set the Nix sensor to alert me when I’ve sweated a certain amount and need to replace fluids. The sensor doesn’t track my hydration state directly, but rather the amount I’m sweating. At the end of my workout, Nix updates my sweat profile and recommends the best rehydration brand for my sweat profile.

Nix also provides an environmental profile that includes factors like temperature, humidity, solar load, wind, and altitude, and scores the impact of the environment on my sweat range. This is helpful for setting my expectations for how much I’ll be sweating during a workout.

Based on my limited testing, the recorded sweat volumes and electrolyte concentrations seem accurate and comparable to what I’ve learned from other hydration tracking methods. However, there are a few downsides to consider.


nix biosensor garmin ciq app drink alert (3)

As of January 2023, Nix only supports its Garmin CIQ app in the Garmin environment, and you have to have your smartphone with you to see live values. This is not very practical for race day or structured workouts. The workout data is cached, but the live prompts are one of the key features of this product, so a cache is not ideal. The same situation occurs with the Apple Watch, where you have to use the Nix Watch app and carry an iPhone. This is an inconvenience, especially if you bought the Apple Watch Ultra with LTE connectivity.


Another downside is the cost – at about $/£6 per sensor patch, it can become very expensive to use regularly. The initial cost of the sensor is reasonable, but the ongoing cost of use is too much for me. I compared it to a top-end heart rate monitor that costs around $/£100-$/£150 and would last for 1000 workouts, making the per workout cost a few cents, while £/$6/patch is a significant increase in the cost of my workout. While proper hydration management is important, I’m not sure if Nix has found the right balance in terms of pricing. Pros may not mind, but for the average person, it could be a bit steep.

More: for $129 (£109) complete with 4 patch refills which otherwise cost $25 (£22).


  • Realtime view of a key performance metric
  • Realtime hydration prompts
  • Analysis of the optimal rehydration brand for your sweat type
  • Securely and easily attaches


  • Relatively high ongoing per-unit cost @$6
  • Does not link to a Garmin CIQ data field (only a Garmin CIQ app – this will change)
  • A smartphone must be present to see live hydration data on Apple or Garmin
  • Sweat data doesn’t start to show for about 20-25 minutes
  • Single-use/36-hour patch
  • Cannot be submerged in water

Nix Biosensor – Unboxing, Contents and How it works

Along with a USB-C powered charging case, you get the Nix Biosensor and four single-use patches.

how to wear a nix biosensor for this hydration review

The patch goes on your biceps and is based on KT tape and so adheres extremely well. I cleaned my skin with rubbing alcohol first. The Nix Biosensor clicks on the patch and immediately starts to calibrate itself. It will take up to 25 minutes to start showing your sweat stats (volume and electrolytes).

There is no needle. Nix is 100% non-invasive.

When you’ve finished and pulled the patch from your skin, you’ll feel that the underside of the patch is damp with your sweat. Throughout your workout, a small amount of this sweat is moved and channelled through electronic circuitry and bioelectrically analysed. The end result is that your sweat rate, electrolyte loss rate, and sweat composition are measured in real-time.

Those base metrics are then broadcast using Bluetooth and it’s worth noting that you do NOT get your hydration status, just your sweat rate (and composition)

Q: Can I wear it somewhere else other than my biceps?

A: Yes (but don’t). The biceps is one of the best places for good adhesion and the ability to extrapolate full-body results.


Using the Biosensor

The Nix Biosensor is kinda easy to use…and kinda NOT easy to use at the same time. Let me explain.

You first have to pair every Nix biosensor with the app. That’s easy enough and broadly works how you’d expect. There are various messages that say you might not see any data for 25 minutes (which is fine) but is it really working? I mean really working. If you set out on your ride you’ll be a long way from home after 25 minutes and if, for some reason, the numbers don’t start coming through there is nothing you can do about it. I’ve kept a patch on and tried to re-use it the following day (within the 36-hour period) and you get the same message that all will be fine in 25 minutes. Everything wasn’t fine, there was no data as the patch had effectively expired the previous day.

My lack of certainty about whether or not everything was working was compounded on the occasions when I had made a mistake and erroneously started a recording. Now, the patch is sold as a single use so if I stop recording can I start recording again? or is that a second use? What if I do that a third or fourth time? I put this to Nix several times and they said it should be OK but after repeatedly trying to get clarification I couldn’t get them to say in exactly what scenarios and for what duration the Nix would work eg 3 false starts.

When you want to use the Garmin CIQ app then you have to start both the CIQ app and the smartphone app and they always need to be close to each other. So you press ‘start’ on both except the CIQ app doesn’t really start until the patch starts to send data ie 25 minutes later.

Then this 25-minute factor causes more annoyance. Let’s say you cleverly decide to start it running 25 minutes before your head off on your run/ride. Assuming that you are sweating a little bit already then that’s not too bad an idea however on one occasion I’m pretty sure the Garmin watch I was wearing and the smartphone temporarily lost contact during a coffee stop. They did seem to re-establish contact but I lost over an hour of the workout on the app and that matters because the reported sweat rates need a reliable measure of duration.

Using Nix with a smartphone

How many Ironman athletes are going to run or ride and take their phones with them? Some will perhaps, but none will during a race as it’s not legal and the same applies to marathons.

I see quite a few casual runners near where I live and many DO run with a smartphone whilst listening to music. Very, very few of them are the kinds of athletes who would ever buy a relatively expensive sweat sensor. Yet the requirement to carry a smartphone for Nix to work seems to imply to me that it’s designed to work for precisely those people ie from a technical perspective it seems to be designed for Fitness users, not athletes – obviously, from a physiological perspective it’s clearly designed for athletes.

Maybe you could argue it’s designed for cyclists, many of whom do carry a smartphone, let’s talk about them, they all own a Garmin (or Wahoo).

Using With a Garmin

Garmin Instructions:

It’s fairly reasonable to assume that many serious cyclists use Garmin Edge bike computers and that a fair proportion of those will take a phone with them.

Keen cyclists who are going to be cycling for many hours absolutely WILL be concerned about hydration (I am, you are) and may well be an excellent target market for Nix (I am, you probably are). They’ve probably got mid-range to top-end bikes, expensive wheels, a power meter and more besides. So they start the Nix app on the smartphone and the CIQ app on the Edge. Except then there’s a problem. The CIQ app (it’s not a data field) entirely takes over the running of the bike computer and does not pair with power meters. Most of the readership here has a power meter by now, right?

So a pretty good cyclist going for a 100-miler absolutely WILL be able to see live hydration alerts but will have no idea of power output nor will they be able to follow a Garmin structured workout when indoors sweating away on the turbo trainer.

nix hydration review biosensor garmin ciq app summary

Note: Nix is close to completing work on a CIQ data field. That WILL solve the Garmin usage problem but will likely deliver less functionality than Nix’s app.

Using Nix with an Apple Watch

In principle, things are similar here with how the product works on Garmin. Both the iOS app and Nix Watch app need to be linked. Plus the Nix Watch app needs to be the one that runs throughout your workout. Let’s put to one side the fact that the fonts on the Watch app are unreadably tiny as that can be easily changed.

Apple Watch athletes are more likely to be runners than cyclists and if they do cycle many will already have another bike computer.

Runners with the Apple Watch might be used to using different apps to log their workouts. However, if you are a regular user of iSmoothRun, the adidas or Nike apps, or even the Apple Workout app then you will have to instead rely on the Nix Watch app to record your workout and guide you through it. The workouts are still saved in Apple Fitness and you can still listen to music.


In response to Nix’s hydration alert, a simple swipe or button press on the app is all you need to confirm that you have replenished. You don’t have to have the drink as it won’t affect the readings but replenishment is shown later on the workout summaries.

The obvious problem here is that the phone might be in a cyclist’s back pocket. When Nix release a Garmin Data Field I’m fairly sure they won’t be able to include replenishment functionality in the data field (unlike its app).

Nix Hydration Alerts

If you regularly use Nix, the most useful feature is a SMART hydration reminder. Nix is different to other hydration support strategies you may have previously used which will probably be simply based on time-based reminders that, even if you are lucky, might attempt to estimate sweat loss based on exertion, sport type and environmental conditions. Nix actually MEASURES what you sweat and thus can alert you to replenish what you have lost.

You might be a sipper or a guzzler. Either way, Nix can remind you to sip/guzzle/drink once you have reached a level of sweat equivalent to the amount you are going to drink.

Sweat Composition & The Nix Smartphone Hydration App – Review

The app is relatively simple but well-designed in and of itself.

Here are some representative screens that you can see on the app outside of a workout. You can see there is some interesting stuff plus the basics that simply report what happened in the workout. I’d like to draw your attention to the more interesting insights provided by the app.




First up on the interesting front is your sweat profile comprising your: sweat rate; electrolyte loss rate; and sweat composition.

You can easily see how the sweat composition of 2.39 mg/ml tallies with the LMNT beverage on the sweat composition chart of all electrolyte beverage brands.

The sweat rate is seemingly obvious at first sight but more nuanced when you’ve thought about it. My sweat rate shown above of 415.7ml/hour is based on a 105-minute run so maybe I cannot extrapolate that rate to a 3-hour run, not to a 3-hour ride and maybe I can’t extrapolate it either to the same run in midsummer. Thus NIX introduces its proprietary Nix Index, shown above as 56% if I started a workout immediately, this 56% means that my sweat range would be my average ie not especially influenced by the conditions



Q: Is the Nix Biosensor Accurate?

A: Yeah, I’ve no reason to think it isn’t. Here are my thoughts on why #NotScience

There are two things to test here 1) sweat composition and 2) sweat volume. The former is very difficult as I’ve got nothing as detailed to compare with. However, I have done sweat tests in the past that have shown that I have more than averagely salty sweat plus, anecdotally, in my Summer HIM races I invariably finish with an inch-thick layer of white salt covering most of my tri-suit (well…almost)

Sweat volume is a tad easier to measure in principle but involves nudity so more sensitive readers should skip to the next chapter right now.

To determine how much you sweat you need to weigh yourself naked before and after a workout. The difference is almost entirely due to sweat loss. Thus if you lost 1kg you will have sweated 1 litre. If you consumed gels or other liquids, you’ll need to add the weight of those liquids (and not their containers) to the starting weight and if you decide to urinate you’ll have to measure it in some way….so try to avoid doing that! A final problem here is that my Garmin Index S2 smart scale may not be super accurate, I took a couple of readings before and after the workouts just to be sure.

Workout 1 (Bike):

  • Nix Says: 813.8ml
  • Garmin scales say: 800g (knock 40g off for a gel)

Workout 2 (run):

  • Nix Says: 650.6ml
  • Garmin scales say: 700g

Workout 3 (Cycle):

  • Nix Says: 693.8
  • Garmin scales say: 700g

So I reckon it seems about right. If we extrapolate that it is ‘about right’ over short time periods then the recommended amount to refuel/rehydrate (sip) should also be about right. I would say that it was likely that you could follow Nix’s DRINK recommendations and keep your hydration state within 1 or 2% of the starting state and that’s all you need to do to avoid performance hits due to dehydration – providing you have the right electrolyte consumption as well but we’ll come to that.

A Nix validation study showed that its recommendations kept athletes within 1% of their starting body mass. Performance loss, according to Nix, starts to happen at 2% body mass loss.

nix hydration review biosensor

FAQ – Frequently Asked Questions (Nix Hydration Review)

Here is a combination of frequently asked questions and more obscure ones. Entertainment for the technically minded.

Q: Can I use Nix in a triathlon?

A: No. Nix is water resistant but the patch will not work if submerged in water

Q: Does Nix cache my workout data?

A: Sort of. It fully caches its sweat-related data. That will sync back to your phone should you forget to take your phone with you on a workout.

Q: Does Nix work on platforms other than iOS, Garmin and Apple?

A: No. As of Jan 2023. Nix claim to be working with other companies, probably Wahoo would be the next to get involved.

Q: Is there a Garmin CIQ data field?

A: No. As of Jan 2023

Q: When does Nix start measuring?

A: Nix requires 0.0045ml of sweat for a first reading which will usually take a minimum of 10 minutes but perhaps 15 minutes or as long as 25 minutes. It varies.

Q: What is the life of a Nix patch?

A: Nix patches are sold as single use however the website also claims 36 hours.

Q: Are there voice notifications?

A: Yes via the Announce feature in Siri. ( Settings > Notifications. Scroll down to “Siri”. “Announce notifications=On”.

Q: Can I share a nix?

A: You can share the reusable sensor but not the single-use patches. Removing a patch will damage it.

Q: How long is the Nix Hydration Biosensor’s battery life review?

A: 24 hours on a full charge

Q: Who is the target market?

A: Nix state this if for athletes exercising more than 45 minutes and for more recreational level sports people undertaking much longer exercise – I’m somewhat doubtful of the 45 minute expectation because Nix takes 25 minutes to start showing results (Nix will say their algorithm accounts for that period)

Q: Can I export my workout data to Training Peaks or elsewhere?

A: No. The hydration stats are not currently recorded as CIQ developer fields nor are they recorded into Apple Fitness/Health

Q: Is Nix ANT+ compatible

A: No. It has a proprietary Bluetooth connection

Q: Is Nix likely to be incorporated into other apps such as iSmoothRun on Apple Watch?

A: No. As things currently stand calculations are made on the smartphone app and it’s not simply the case that an app can comply with the BLE signal from the biosensor

Q: How do I turn Nix off?

A: Simply take it off the patch and Nix turns itself off

the Nix Hydration Review – Summary & Thoughts of sports latest biosensor

As of January 2023, Nix has just hit the market for the first time. For a new product, it shows promise and with a bit of tinkering, I could see myself using it in anger once the weather hots up.

As endurance athletes, most of us have had times when we’ve known that we’ve been less than optimally hydrated and probably other times too when mild dehydration wasn’t too noticeable but probably impacted our performance nevertheless. My own efforts to drink more and stay hydrated may have resulted in over-drinking and time lost for comfort breaks. It seems obvious that an accurate replenishment strategy is going to work wonders for most of us. In a way drinking the right volumes of the right degree of salty water and the right intervals is a relatively easy and effective ‘quick win’ – a much quicker win than getting to grips with blood sugar via Supersapiens, muscle oxygen via Moxy or cDa tinkering with Notio.

From what I’ve read about the technology and from what I’ve heard from competitors who’ve not yet come to market, this kind of technology should be actionably accurate and my limited testing and experience seem to support that.

So far so good.

The ‘but’ comes in how the product has been technically designed. Nix seem to have overly focussed on getting an app working but initially failed to understand that its target market of athletes just won’t use the product the way Nix may have envisaged. Once a Nix CIQ data field is ready I reckon sales will take off.

This has been a strange review to write. My first draft was unfairly negative because of the technical issues, however, hopefully, I’ve positioned it more positively now in light of some of the big differences that properly measured data will make to us. That said, it’s a bit expensive although I seem to be saying that for every new product at the moment.

Price & Availability – Nix Hydration Review

Nix is only available directly from  for $129 (£109) with a 4-pack of replacement patches costing $25 (£22).


nix hydration review biosensor app





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4 thoughts on “the Nix Hydration Review – Garmin & Apple Electrolyte sport biosensor

  1. Nice but as the supersapiens sensor too expensive for an amateur athlete.
    Anyway these sensors have a deadline timeline. 2 or 3 years till these will be integrated on smartwatches.

    1. i cover when the sensors are likely to become more widely available here:

      I’m not sure if Nix’s exact method will ever find its way to be integrated into a wearable sensor like a ohrm. it would probably have to be done a different way.

      in some ways supersapiens is cheaper than nix! depends on how often you want to use it

  2. if you have working kidneys and functional hypothalamus you don’t need hydration sensor. Only people with the terminal kidney failure and insipid diabetes combined with dysregulation of thirst mechanism need this.

    1. no that’s not true.
      Sports people who lose 2-3% of body mass through sweating during a workout will suffer impaired performance

      even talking about ‘wellness’: one of the bigger killers of the elderly in UK hospitals is dehydration. OK this product isn’t intended for that market but it illustrates the need to stay properly hydrated

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