Are Smartwatches Accurate in Detecting Stress? New Research Reveals Limitations

Smartwatches have become an integral part of daily life for many, with over 455 million users worldwide in 2024. These devices are particularly popular among young adults aged 18 to 34, where approximately 40% utilize them to monitor various health metrics. Among their features, smartwatches assess heart rate and interpret biometric data to provide insights into sleep quality, fatigue, and stress levels. However, recent scientific studies cast doubt on the accuracy of these stress measurements.

A notable investigation led by Eiko Fried and colleagues at Leiden University evaluated the reliability of smartwatch-derived data compared to self-reported experiences. Over three months, nearly 800 smartwatch users participated in a study where they filled out brief surveys four times daily via their smartphones, reporting their thoughts, feelings, and activities, along with reflections on their day’s peak moments.

The researchers analyzed the correlation between physiological data collected passively by the wearables and the participants’ self-reports of stress, tiredness, and sleep. Surprisingly, the overlap was minimal, especially when it came to detecting stress. In many cases, the smartwatch indicated stress in the wearer, yet the individual did not report feeling stressed, highlighting a disconnect between physiological signals and subjective experience.

One key reason for this discrepancy is that most wearables infer stress primarily from heart rate and its variability. Fried explained that changes in heart rate alone are insufficient indicators of stress because heightened heart rates can result from a variety of emotional states—fear, excitement, stress, or even arousal—making it hard to distinguish between them solely based on biometric data.

This research raises important questions about the validity of wearable data when it comes to assessing mental states. While these devices provide valuable objective data, Fried emphasizes that they should not be seen as fully objective measures of psychological conditions. Instead, combining wearable data with self-reports can offer more comprehensive insights into a person's mental and emotional health.

The findings also suggest caution for individuals relying heavily on smartwatch feedback to guide their health or lifestyle decisions. It underscores the need for continued research to understand the limitations of biometric data and the importance of subjective reporting. Future studies, such as the upcoming publication of Fried and Siepe’s paper in the Journal of Psychopathology and Clinical Science, aim to deepen our understanding of how passive sensor data relates to actual mental experiences.

In summary, while smartwatches are useful tools for tracking physical health, their ability to accurately detect psychological stress remains limited. Users and clinicians should interpret stress data from these devices critically and consider integrating self-reports for a more holistic view.

Source: https://medicalxpress.com/news/2025-07-smartwatch-youre-stressed-wrong.html