Nix’s Hydration Biosensor is for athletes who sweat the details

That royally sucked. I missed out on valuable long-run data, and long runs are when hydration is most important! Even worse, these are single-use patches, and I’d wasted one. It costs $25 for a refill pack of four, meaning each patch is $6.25. Human error played a large role in this, but better connectivity could’ve at least saved the situation. I made a silly mistake, but not an implausible one.

I get why the sweat patches are single-use. Adhesives never stick quite as well after the first time. Plus, you’d have to wash off old sweat for accurate data, and adhesives break down with water and soap. But knowing this doesn’t stop these patches from feeling wasteful — both monetarily and environmentally. Nix does have a partnership with Terracycle, so you can at least recycle used patches for free. I appreciate the option, but I had to root through Nix’s FAQs to even find out about it, and the whole process requires a bunch of extra steps. People are lazy, and I have a feeling most used Nix patches will end up in a landfill anyway.

While I’m airing my gripes, it’s a bummer that the Nix sensor doesn’t support workout types outside of indoor/outdoor running and cycling. You don’t really need granular hydration data for yoga, pumping iron at the gym, or a short HIIT workout, but it’d be nice for long hikes, other types of strenuous cardio, or outdoor sports. Hopefully, Nix will add support for more activity types down the line.

I was also disappointed to see Nix is iOS-only at the moment. The company says that Android compatibility is slated for this month (February 2023), but it wasn’t available when I was testing the device.

Data fit for Type A athletes

To get accurate results, Nix recommends a sweaty run or cycling session that lasts at least 45 minutes. Once you successfully log a workout, the app spits out a summary that includes the exercise, whether it was indoors or outdoors, and what you used to hydrate. You’ll also see temperature, humidity, dew point, solar load, wind, and altitude. As for hydration metrics, the app will tell you how much fluid and electrolytes you lost during the workout, as well as your sweat composition (aka, how salty your sweat is).

There’s also a more general sweat profile that aggregates data from multiple workouts. There you can see your estimated sweat rate, electrolyte loss rate, sweat composition, and Nix Index, a proprietary score that’s meant to show how sweaty a particular workout was for you.

When I told my spouse about this, they gave me a withering look. It’s the same one they give me whenever I explain a new doodad I’m testing and the data it tracks. It’s derision incarnate. You see, my spouse and I are polar opposites when it comes to fitness data. My spouse is one of those naturally gifted athletes who manage to run like the wind on four hours of sleep and a half-eaten protein bar. They only begrudgingly use an Apple Watch to stream music because they can’t be bothered with offline playlists. They have never once reviewed their workout stats. This sensor isn’t for easy-going Type B athletes like my spouse.

It’s for people like me, the Type A doofuses that use color-coded spreadsheets for training logs and set out their workout clothes the night before. The nerds who look up and compare multiple training plans and energy goo nutrition labels before settling on one. The ones who look in the mirror and think, “I, a quantified sicko, can be optimized for maximum performance.”

I’m fully aware that I don’t need Nix to run a well-hydrated 13.1 miles. I’ve run plenty of races before I ever tried Nix and have always crossed the finish line in one piece. But I also know I can do better. I appreciate knowing I sweat about 7.8 ounces of fluid and 365mg of electrolytes per hour in the winter. I like knowing I should use a sports drink with roughly 47mg of electrolytes per ounce. You can do the math yourself, but it’s a headache. Sports drink companies don’t make it easy to figure out and compare electrolyte levels, and marketing tends to focus on carbs instead.

That’s why it’s cool that there’s a handy chart right in this app I can reference that lets me compare electrolyte levels of popular sports drink brands. Turns out Liquid IV is the one that most closely matches my electrolyte needs. It’s not hard proof, but anecdotally, my training has improved since I coincidentally made the switch from Maurtens a few months ago. I will 100 percent use this information when I’m preparing my next long run.

The bottom line is it helps me plan my runs, which in turn alleviates my anxiety about completing said runs to my ridiculous and arbitrary standards. If planning helps you feel more confident about a run or a biking session, then there are a few scenarios where I can see the Nix sensor being a worthy investment.

For example, if you’re a triathlete who frequently races in all sorts of climates. The Nix could be helpful in fine-tuning your hydration strategy whenever you train in an unfamiliar environment. Or, if you’re particularly heat sensitive, this might help you increase summer mileage safely. People just starting to tackle longer distances could also benefit. Personally, I’d have liked a starting point when I was new to hydration and fueling strategies.

But paying $130 for a sensor and $25 for patch refills is a lot, especially since you’re not going to be wearing a patch for every workout. For most people, this is most effective as a benchmark tool that you break out when the weather, your environment, or your training regimens change. A little extra to give you a slight edge. That’s the thing about gadgets like these. They’re not essential. They’re a “nice to have” if, and only if, the expense makes sense.

If you’re sold on the idea of hydration patches and trying to decide between this and Gatorade Gx patches — just go with Nix. It’s more expensive up front, but in the long run, you get four patches in a $25 refill compared to two. It’s also more thoughtfully designed, works reliably, and gives you more actionable data. It’s what Gatorade was trying to do, but better.