Wearables Want To Track Your Stress — But It’s Really Hard To Do

Measuring stress, one of the hottest trends in quantified mindfulness, is much more challenging than it sounds.

If you’re someone who stresses out, a wearable that reminds you to chill when you’re on edge might sound like an ideal gadget. You’d be able to review your body’s data and understand what fuels your anxiety each day (Work deadlines? Morning traffic? Game of Thrones cliffhangers?). And maybe, empowered by this information, you’d learn to keep calm in stress-inducing situations.

Spire, a stone-shaped tracker that’s coming to Apple stores July 12, joins a growing number of wearables and apps that promise to help you manage your stress. The startup behind Spire, and others like it, say their technology can help improve your mental health and overall well-being. Apple’s in on it, too: Just last month, it unveiled the Breathe app for the Apple Watch, which promotes mindfulness by prompting you to take deep breaths.

But there is scarce evidence that meditation and mindfulness apps actually have health benefits. And while there’s little harm in being prodded to breathe more deeply more often, customers may not realize just how hard it is for a portable machine to accurately detect their real-time stress levels.

“Measuring stress has been a holy grail,” Dr. Santosh Kumar, a computer science professor at the University of Memphis who has studied wearable sensors’ ability to measure stress, told BuzzFeed News.

“There [are] so many things you can do if there was a way to measure stress reliably in a field environment,” he said, like figuring out which jobs and everyday activities are most stressful for people. “[But] getting quality data — continuously, passively, when no one’s observing you, when you’re engaged in a free-living environment — is extremely hard.”

What’s breathing got to do with it?

Spire’s stress-tracking device, which sells for $129.95 and has been available until now through online stores, clips to your belt or bra to detect your chest’s motion as you inhale and exhale. The data feeds into an app that illustrates your breathing wave in real time, deduces how much you normally breathe in a minute, and breaks down your breathing patterns into “calm,” “focus,” and “tense” minutes.

Stress sometimes manifests psychologically, sometimes physiologically, and sometimes both. That's why it's so hard for wearables to track.

You are “tense” when, after a two-minute period, your breathing registers as faster and more erratic than the way you usually respire, according to Spire’s executives. When this happens, the app sends you real-time notifications about your status and suggests audio-guided breathing exercises, from reducing tension in 30 seconds to meditating for eight minutes. While Spire’s definition of “tense” may cover stress in the traditional sense, it can also encompass moments of excitement, or even miss your silent freak-outs if your breathing patterns don’t change.

That’s the challenge for all wearables that set out to externally measure stress, a condition that sometimes manifests psychologically, sometimes physiologically, and sometimes both.

“Stress is not a bad thing,” said Spire’s co-founder Neema Moraveji, who used to direct Stanford University’s Calming Technology Lab. “You can feel excited and be having a really excited conversation with someone and your breathing is quite tense, and Spire will show you had a tense breathing streak. You can say, ‘Oh, my breathing was tense — was that a bad thing?’ No, it was actually good. But you’re creating awareness for the person: ‘I guess I’m amped up right now.’”

Breathing is just one biometric that scientists have studied in the hopes of measuring stress; others include sweat, temperature, heart rate, blood pressure, and blood volume. Each has its strengths and weaknesses.

The body reliably breaks into sweat in situations that trigger a fight-or-flight response, but some of the key sweat glands are on our palms and feet — which, Kumar noted, are tricky places to stick a wearable sensor. And it’s hard to measure fluctuations in body temperature, which tend to be very small and highly subject to environmental factors, Kumar said.

In a 2015 paper, Kumar and a team of researchers concluded that the best metrics are a combination of heart activity and respiration. That said, it’s still difficult to capture accurate, reliable data about someone on the move. A machine that’s constantly in motion and sometimes loses direct contact with the body will likely pick up erroneous and irrelevant information, versus when it's on a person sitting still in a doctor’s office, especially when it comes to tracking heart activity, Kumar said.

Spire’s CEO Jonathan Palley and Moraveji say they focused on breathing because it’s an action people understand and can control much more easily than they can, say, slow down their heart rate. “From a product perspective, if you give people feedback around the thing they can control, then you can close the loop and do something about it: ‘Oh yeah, I’m not breathing this way, I’m going to fix it,’” Moraveji said.

In internal validation tests, Spire is 85% to 95% accurate compared to a spirometer, the official scientific instrument used to measure lung capacity, according to Moraveji and Palley. But the startup has not published peer-reviewed research about the accuracy and reliability of its device.

Moraveji and Palley said that studies done with Spire over the last six months are expected to be published by the end of the year. “The fundamental idea behind Spire is to use validated research around respiration and make it more accessible to consumers,” they told BuzzFeed News.

What else can you track?

Other stress-monitoring wearables track the electrical activity in your skin, which upticks when your body’s sympathetic nervous system, the driver of flight-or-fight response, kicks in. These devices include the Pip, a gadget designed to be routinely held between the thumb and fingertips. Neumitra is developing sensors that measure this activity as well as heart rate, which can be integrated into commercial wearables such as traditional watches.

There’s a limit to what your wearable can tell you. Machines can’t read minds.

Another startup, Empatica, has an Embrace wristband that also aims to track your skin’s electrical activity, among other metrics, to detect stress. It’s being tested along with an app in clinical trials to alert for help when a person has a seizure, which manifests with significant changes in skin's electrical activity. Empatica is seeking the Food and Drug Administration’s approval to sell it as a medical device. (A similar Empatica device has already won the equivalent agency’s approval in Europe.)

Empatica’s chief scientist, Rosalind Picard, started developing the device after she co-authored an award-winning study in 2004 that strapped sensors to car drivers to test their stress levels. She and her research team have gone on to publish other papers in support of the idea that Empatica’s wearable can collect accurate data.

But most stress-tracking wearables are not scientifically rigorous, Picard said. “A lot of the people jumping on the consumer bandwagon claiming things — you’re not going to find them getting through the FDA,” she said. And she’s right. So far, few wearable makers, whether they track stress or some other biometric, have released peer-reviewed research or sought FDA clearance to back up the purported health benefits of their products.

Maybe an FDA stamp of approval isn’t all that important to you. But if you are indeed in the market for a gadget to quantify your stress, just remember that there’s a limit to what your wearable can tell you. Machines can’t read minds.


Empatica’s Embrace wearable is being tested as alert system for when someone has a seizure. An earlier version of this post said the wearable was being tested to detect seizures before they happen.

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