Smartwatches continue to incorporate “life-saving” technology such as fall detection, SOS calls, atrial fibrillation warnings and the latest Loss of pulse feature on Pixel watches, all to keep you feeling safe. But there's a less flashy, more common concern that most watches treat as an afterthought: tracking hydration and sweat loss.
I've been wanting better hydration tools on watches for a while, but last weekend's report from 35-year-old runner Bobby Graves, He died of cardiac arrest after finishing a half marathon at Disneyland Last weekend, a day after I self-diagnosed myself with heat exhaustion at 38ºC, it hit me.
This man was my age, had run several half and full marathons in the past, and was not at an age where people worry about heart health. Maybe the medical report sheds light on the extenuating circumstances, but there's a reason the expert cited by SFGate specifically warns people to “make sure to stay hydrated” during hot weather.
Smartwatches have the means to calculate sweat loss during workouts – Samsung even claims it’s clinically accurate at that task. But most other brands (aside from Garmin) ignore it, and those that do track it don’t take sufficient advantage of it.
I would say it is about time that hydration becomes a priority for fitness brands. Excessive heat will only get worse over time and watches need to be prepared for it.
Hydration tracking is the most basic thing you can do.
Both Wear OS and WatchOS have some water tracking apps like Water Reminder and Water flameSamsung's One UI Watch has its own hydration tile, and Garmin watches let you download a snapshot of hydration tracking from the Connect IQ store.
They vary in appearance and specific functions, but they all work pretty much the same way: You open the app or tile and tap a button to indicate that you've had a glass of water. The screen will show how many ounces of fluid you have left to drink that day. You can also set periodic reminders to check in on whether you've been drinking.
It's pretty useful for everyday life! But that daily reminder to drink water doesn't take into account context, like how hot it is or whether you've exercised; you'd have to change the goal yourself. And the combination of drinking every hour and movement reminders They can be so annoying that most people ignore or disable them.
Some sports watch brands like Coros and Polar let you set reminders during training activities to refuel or rehydrate, but at preset intervals — again, there’s no context about how much water or electrolytes your body actually needs.
Ideally, a watch would detect when the user has sweated (or is sweating) more or less than usual and dynamically suggest that the person drink more water to avoid problems with dehydration and heat exhaustion.
Accurate sweat tracking IS possible with smart watches
Earlier this month, Samsung he boasted that a clinical study from the University of Michigan demonstrated the accuracy of its Galaxy watches compared to medical-grade sensors for heart rate (90%), VO2 Max (82%) and sweat loss (95%). That's pretty much what I expected from a Wrist-based optical heart rate sensorbut the precision of the sweat surprised me.
Samsung doesn't track sweat loss directly. It makes an estimate “based on your body size, age, gender, and the intensity of your workout, including heart rate, ambient temperature, and other conditions.” I had always attributed my sweat loss to weight loss. Galaxy Watch UltraThe sweat loss figures after running are a guess, but they are apparently educated guesses.
The only one straight The consumer sweat loss tool I'm familiar with is the Nix Biosensor. It attaches to your bicep and sends sweat through an “inlet” with electrodes on either end, calculating its “velocity” to determine your sweat rate. It then extrapolates how much sweat the rest of your body loses, since different parts of your body have different sweat rates.
Nix's sensors are potentially useful for serious exercisers, and I intend to test them for an upcoming column. But they're niche and only used in exercise concepts; we need mainstream smartwatches that are worn daily to be the authority on sweat.
He Pixel 3 watch The cEDA sensor can detect “small changes in the level of sweat on your skin” to provide data on stress, but I don't think it's designed to track total sweat loss. Apple patented a perspiration sensor This would “measure the amount of fluid lost over a time interval” and even show a real-time rate of sweat loss, but a patent is no guarantee that a company can make a concept work in real life.
For now, I'd be happy if more brands imitated Samsung and Google, using your standard heart rate and body data to estimate sweat loss after workouts. However, over time, they'll have to go even further, in line with what Apple patented.
Picture this: Let's say you're running a half marathon with a Galaxy Watch 7 In warm conditions. During the run, a data screen will show in real time how much sweat you're estimated to have lost, perhaps calculating the new total every few minutes or every mile. At certain thresholds — perhaps every 500 ml of sweat loss or a customizable number — it might vibrate on your wrist suggesting you refuel soon.
If your body's sweat rate slows down If you're running, that's a serious sign of dehydration. Your Galaxy Watch will warn you to stop immediately and rehydrate or seek medical attention, just as it will alert you if it detects arrhythmia or low heart rate.
Once you've crossed the finish line, the watch will give you an estimate of your total sweat loss, just as it does now. But it will also automatically add your lost sweat totals to your Hydration box. Samsung recommends that you “replace 150% of what you lost in 1-2 hours,” so I guess you could easily multiply the total milliliters of sweat lost during your workout by 1.5 and add the fluid ounces in there.
So maybe you could send post-workout notifications at the one- and two-hour marks, reminding you to log your total water intake in the Hydration tile to confirm you're refueling properly.
That’s my vision of how this could work. Ideally, the sweat sensor wouldn’t just activate during workouts, but would measure sweat continuously (like Fitbit’s cEDA sensor) and start tracking more frequently if you hit a certain sweat or heart rate threshold, or if the local climate and humidity are especially high.
It would be useful for farm workers, hot van delivery drivers, construction crews, and many other outdoor workers, not just athletes.
Garmin comes closest to my idealized vision of useful sweat loss data, though it hides the hydration tracking tool in Connect IQ as if it were embarrassed. Once you download it, you can open the app settings and turn on the “Automatically increase goal” option to add sweat loss during training to your standard daily goal.
I tried it on my Garmin Forerunner 965And it added six cups of water to my daily total after I supposedly sweated that amount during a 10K run on a hot day. But Garmin underestimates my sweat compared to Samsung. and It doesn't follow the “replace 150%” advice. I always need more water than Garmin thinks, so it's more useful in theory than in practice.
For the sake of runners trying to keep going and finish races when their bodies are trying to tell them to stop, fitness watches We need to be ready to intervene at any moment, not just tell you at the finish line that you've sweated a river.
Instead of relying on algorithms, it would be better if they started measuring body sweat directly for more personalized data, as reasonably accurate brands like Garmin and Samsung will produce different results with heart rate estimates. With sweat data, warnings to drink water or electrolytes would be more relevant.
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