Steps, stress and sleep: what wearables can measure

The Apple Watch was first introduced in April 2015 as a luxury item. Today, it's FDA approved for several diseases. Tokyo, Japan, April 2015. Keystone

Whether in the form of a bracelet, a pair of headphones or a sensor tucked into your underwear, wearables have become ubiquitous in our daily lives. From blood sugar to apnoea, here are the health stats you can measure with these devices.

Swiss watchmaker Abraham-Louis Perrelet, credited for crafting the world’s first pedometer or step-counter in 1780, would have probably never guessed that a Japanese marketing campaign urging people to take 10,000 steps a day for better health would permanently influence lifestyle habits from the mid-1960s onwards and make his invention ubiquitous.

Today, the number of steps to take in a day is still a driver of health goals (as of 2025, the magic number has been updated to 7,000External link) and the decade-old Apple Watch, once a luxury pedometer, is a medical device approved by the US Food and Drug Administration (FDA) that alerts users External linkif they are experiencing atrial fibrillation, a type of heart arrhythmia.

Last June, US Secretary of Health Robert F. Kennedy Jr. announced External linkthe launch of the biggest advertising campaign in the history of the US Department of Health and Human Services, encouraging the use of wearables.

Kai Reusser / SWI swissinfo.ch

The medical device industry is projected to more than double from $60.9 billion (CHF49 billion) in 2024 to $162.7 billion in five years, according to Grand View ResearchExternal link. An array of niche trackers and data have popped up in recent years: Garmin smartwatchesExternal link and Whoop braceletsExternal link can calculate a person’s daily energy reserves, while Neurable’s headphones can determine levels of focusExternal link by tracking brain activity via an electroencephalogram (EEG). Here’s the health data you can track with consumer wearables.

Heart rate

Nearly all wearables track heart rate, in some instancesExternal link replacing electrocardiograms (ECGs) performed at the doctor’s, where electrodes are placed on a patient’s chest.

Although not as reliable as ECGs, wearables are catching up with professional measuring tools. Keystone

Wearables can determine the resting heart rate (RHR), between 60 and 100 beats per minute in healthy adults, and heart rate variability (HRV), the variation between heartbeats (usually fractions of seconds). The faster a heartbeat adapts to change caused by stress or exercise, high HRV, the healthier the user. Temperature, motion, RHR and HRV can also help determine the wearer’s stress levels.

Wearables use photoplethysmography (PPG), an optical sensor that illuminates the skin to measure heart rate by detecting changes in light absorption and blood volume variation.

Blood pressure

High blood pressure, which can cause heart attacks and strokes, is often referred to as the silent killer because it shows no symptoms but affects 30% of adultsExternal link. Watches measure both the pressure in arteries during and between heartbeats.

While Japanese healthcare solutions provider Omron and Chinese tech giant Huawei manufacture wearable watches that use the traditional inflatable cuff in their strap, Swiss company Aktiia’s Hilo was the first FDA-approved over-the-counter wearableExternal link that used a PPG sensor to measure hypertension in July 2025 (the most recent Apple Watch now also boasts that featureExternal link).

Sleep

For sleep data, wearables track body movement, temperature, RHR, HRV and respiratory rate (the number of breaths per minute, derived from heart rate data). Results are divided into awake time, non-rapid eye movement (NREM), and rapid eye movement (REM) phases.

While NREM represents about 80% of all time spent sleeping and includes light sleep (when the body switches between cycles) and deep sleep (when muscles repair themselves), the REM stage benefits learning and memory.

A more recent metric is oxygen saturation (also known as pulse ox, SpO₂), tracked by PPG sensors that assess a user’s blood colour. A level below 92% may signal apnoea and affect daily “sleep scores”, which combine several data and determine sleep quality. Finnish wearable company Oura’s smart ring is considered one of the best trackers with about 80% accuracy compared to polysomnography (PSG), a medical-grade test that tracks EEG, eye movement, muscle tone, heart rate and breathing.

Users mostly collect data for their private use in the hope of improving sleep quality, but some experts warn about orthosomnia, a phenomenon that designates obsessive behaviour around achieving perfect sleep scores.

Instant fertility and sugar levels

Swiss-company Ava’s bracelet was one of the first wearables able to identify ovulation in real time by tracking pulse rate, breathing rate, sleep, HRV, and temperature. Today, products such as Canadian start-up Fibra’s smart underwearExternal link are also being developed to track a wider spectrum of female data in real time.

Tracking glucose to avoid spikes that can lead to fatigue, heart disease or diabetes has also become popular in recent years thanks to continuous glucose monitoring (CGM) devices that offer instant data. Although small, tracking patches remain slightly invasive because a needle is required to pierce the skin, making the tool difficult to take on and off. Swiss start-up Liom is developing the first non-invasive CGM device, which it hopes to get to consumersExternal link by mid-2027.

Although technically a wearable, continuous glucose monitors (CGM) can’t be removed and put back on as a small needle needs to be in touch with the user’s blood. Keystone / Christian Beutler

So what’s next for biomonitoring? Non-invasive patches that analyse sweat and measure fluid losses (alongside electrolytes, glucose and cortisol) are currently garnering attention. Australian diagnostics company Nutromics goes one step further with a patch equipped with multiple microneedles to track several biomarkers, just like a blood test, but in real time. Their first “lab on a patch” is expected in 2027 and will first target clinical use.

According to McKinsey’s 2024 Future of Wellness surveyExternal link, consumers will continue taking a greater role over their health, with at-home diagnostics and an increased use of wearables.

Edited by Virginie Mangin/ts