A new study challenges the belief that smartwatches can measure stress with accuracy. Researchers from Leiden University in the Netherlands tested the Garmin Vivosmart 4 in real-world conditions. Over three months, more than 800 young adults wore the device each day. As a result, the team could directly compare stress readings with how participants reported feeling.
The results were clear. There was no strong link between smartwatch stress scores and actual stress levels. In some cases, people flagged as “stressed” reported feeling calm. Meanwhile, others who felt tense showed no spike in their watch data.
Lead researcher Eiko Fried explained why. Most wearables rely heavily on heart rate and heart rate variability (HRV) to estimate stress. However, a racing heart can result from excitement, fear, attraction, or even caffeine. “If you’re in love or giving a speech, your heart might race,” Fried said. “That doesn’t mean you’re stressed in a bad way.”
The study did reveal areas where the devices performed better. Sleep tracking proved more reliable, as about two-thirds of participants said the watch’s sleep data matched how rested they felt. Fatigue tracking showed a weaker but still noticeable link.
What This Means for the Future of Wearables
Fried urged smartwatch makers to be more open about how they calculate stress scores. Furthermore, he recommended using additional biometric signals, adapting readings to each user, and presenting results in plain language. Without these improvements, people should treat stress readings as guides, not medical facts.
Smartwatches still hold value for tracking workouts, steps, and sleep patterns. However, when it comes to mental health insights, they fall short. Future advances may come from AI-driven devices that combine multiple sensors—such as skin conductance and temperature—alongside HRV. With better context and richer data, these tools could become far more reliable. For now, self-awareness and personal reflection remain more trustworthy than a score on a watch screen.
