Smartwatches and activity trackers have become essential tools in the wellness sector for monitoring steps, exercise, sleep, and other health indicators. According to data published by Spain's National Markets and Competition Commission (CNMC) in November 2024, approximately 34.8% of smartphone users in the country utilize these devices. However, beyond physical activity monitoring, researchers are now investigating the extent to which these gadgets can provide insights into a user's mood and emotional state.
A study published in July 2025 in the Journal of Affective Disorders Reports questioned the ability of these devices to interpret emotions accurately. The research examined the relationship between Garmin's stress score and the moods of 95 university students over a 28-day period. While an association was found between the score and certain moods, the results highlighted a critical limitation: measuring physiological activation is not equivalent to identifying a specific emotion. Björn Siepe, a psychologist and co-author of the study, explained that Garmin's stress index relies on heart rate patterns and activity data processed through a proprietary algorithm. Consequently, the device registers physiological activation and labels certain levels of this activation as stress.
Experts emphasize that while these devices offer useful information on measurable physiological indicators like step count or heart rate, they do not measure emotions directly. Siepe noted that a smartwatch infers stress based on bodily measurements such as an accelerated heart rate. However, a faster heartbeat can result from excitement regarding a decision, sexual activity, or an animated conversation without the individual actually feeling stressed. Furthermore, when the watch detects physical exercise, it does not provide a stress score at all.
Physiological activation describes the degree of the body's response, such as an increased heart rate, whereas feeling stressed is a subjective experience dependent on how demanding or threatening a situation appears to the person. A single heart rate pattern can correspond to vastly different states of stress, meaning these physiological signals offer limited information about subjective experiences. To address this, some applications allow for voluntary emotion logging. For instance, the Mindfulness app on the Apple Watch enables users to record momentary emotions and daily moods. These records can be cross-referenced in the iPhone Health app with factors like sleep, physical activity, or daylight exposure to identify patterns, though these associations do not prove causation.
A more recent investigation published in March 2026 in Biomedical Signal Processing and Control addressed the use of wearables for measuring stress-related physiological responses. The report concluded that while these devices can help track specific physiological responses, measurement consistency varied depending on the test. Siepe reiterated that a person might feel significant stress with minimal bodily reaction, while an accelerated heart rate during a stimulating moment might not be perceived as stress at all.
Some Garmin watches now incorporate functions that estimate stress levels based on physiological signals like heart rate variability. To track mood, some applications combine these metrics with voluntary emotion logs to compare them against habits like sleep or activity. Jesús Lázaro Plaza, a biomedical engineering researcher at the University of Zaragoza and co-author of a 2025 study on anxiety and depression monitoring, clarified that feelings are subjective. He explained that data can objectively quantify the state of the Autonomic Nervous System (ANS), specifically the balance between the sympathetic branch, which activates the body, and the parasympathetic branch, which relaxes it. How an individual perceives a specific state depends heavily on the person themselves.
Regarding whether a watch could interpret physiological activation from hiking or sexual activity as stress even if the user feels fine, Plaza confirmed this is possible, especially if the device relies on spot measurements rather than trends. He noted that while sympathetic markers rarely fail to detect an event that has occurred, resulting in high sensitivity, they often detect activations not caused by stress. This leads to false positives and reduced specificity, as the device identifies sympathetic activations that are unrelated to actual stress.
Sources: El País Tecnología.