Your smartwatch might be way off on one key health stat

They’re meant to be your health sidekick, you might suspect that there’s only so much that a wearable can tell you about your mental state from taking a pulse reading. If this wasn’t already obvious, new research appears to confirm that your smartwatch might be completely misreading your mood.

A study published in the Journal of Psychopathology and Clinical Science and reported by The Guardian found that a smartwatch often confuses stress with excitement — and could flag you as overworked when you’re actually having fun. Researchers tracked 800 young adults wearing Garmin Vivosmart 4 devices for three months, comparing the watches’ stress, fatigue, and sleep scores with what participants reported feeling at the time.

According to Eiko Fried, an associate professor at Leiden University and lead author of the study, the verdict on stress tracking was that there was “basically zero” correlation. He said his own Garmin has told him he was stressed while working out at the gym or catching up with an old friend at a wedding. “These are consumer devices, not medical devices,” Fried warned.

Fatigue tracking fared slightly better, and sleep readings were the most accurate of the bunch. Two-thirds of participants saw a clear match between their self-reported good nights and the watch logging about two extra hours of sleep. Still, the researchers say these devices are better at measuring how long you slept than how well-rested you actually feel.

The team hopes the findings will help guide future work on using wearable data for early warnings about mental health issues like depression. But for now, they caution against taking stress scores too seriously — think of them as a rough guide, not a definitive read on your emotional state.