Smartwatches fail to accurately measure stress levels: Study

A new study from the Netherlands has found that smartwatches are largely unreliable in detecting stress levels, raising concerns about their use for health-related purposes. 

Researchers emphasized that these devices should not be treated as medical tools.

The research, conducted by Leiden University, monitored 800 young adults over a three-month period. Participants were asked to self-report their stress, fatigue, and sleep quality four times a day, while simultaneously wearing smartwatches that tracked physiological data.

The findings revealed an almost “near-zero” correlation between smartwatch stress readings and participants’ reported experiences. In fact, for one in four participants, the devices frequently indicated the opposite of what they felt—showing “no stress” when they reported feeling stressed, and vice versa.

While fatigue measurements were found to be somewhat more accurate, and sleep duration data more closely matched participants’ reported sense of restfulness, researchers noted that smartwatch sleep tracking only reflects duration, not sleep quality.

“Not Medical Devices” Warning
Associate Professor Eiko Fried of the Department of Clinical Psychology stressed that relying on heart rate alone to measure emotional state is misleading. “Your heart rate can increase not only due to anxiety, but also from excitement or happiness,” Fried explained.

He warned users against overinterpreting smartwatch data: “Be cautious and don’t live your life according to your smartwatch. These are consumer products, not medical devices.”

The study was published in the journal Journal of Psychopathology and Clinical Science.