The study dismissed the smartwatch’s stress tracking – purely speculation

A study was conducted at Leiden University, In a study involving nearly 800 young people who monitored their stress, fatigue, and sleep for three months using the Garmin Vivosmart 4 smart watch, participants reported their well-being four times a day, and these subjective assessments were compared with the readings produced by the device.

The results showed that stress measurements had practically no connection to the users’ own experiences. Kello often reported elevated stress levels in situations where participants did not experience any stress at all – for example, in the company of friends or during a physical activity session.

Instead, the amount of sleep was recorded much more reliably. In most cases, the watch was able to estimate the amount of sleep with a precision of 1–2 hours compared to the users’ own estimates. However, the accuracy in assessing recovery and the different sleep stages was significantly lower. This suggests that the device functions better as a support for sleep monitoring than as a stress interpreter.

Professor Eiko Fried, who led the research, notes that the smartwatch only measures physiological reactions such as heart rate variability, but cannot assess a person's emotional state. The body's response can rise from joy to excitement to physical strain, but the device easily interprets it as stress.

Industry experts also emphasize that the algorithms in devices are black boxes: manufacturers do not clearly explain how the stress readings are calculated. These are consumer products, not medical devices, and they should not be used for mental health assessment.

• The smart watch tracks sleep very accurately, But stress measurements shouldn’t be relied on too much.

• Results must always be seen in contextPhysical strain or an exciting situation can appear as stress, even if you feel good.

• It is worth listening to one's own feelings more than to the evaluations given by a clock.