Accuracy concerns regarding wearable sleep trackers

Research published in the journal Sleep Medicine has raised concerns regarding the accuracy of popular wrist-worn sleep trackers, such as Fitbit and Apple Watch. Studies involving approximately 2,000 participants suggest these devices often fail to align with a user’s subjective sleep quality, explaining only 2.5 to 16.2 percent of the difference in how refreshed a person feels.

Further findings indicate that these wearables may be unreliable for diagnosing insomnia, showing accuracy in only 39 percent of cases. While trackers showed acceptable agreement with the gold-standard polysomnography (PSG) in 82.4% of healthy sleepers, accuracy dropped significantly among those with insomnia. The devices may overestimate sleep duration by up to thirty minutes and frequently overlook nighttime awakenings if the user remains relatively still. Experts note that technology struggles to account for mental or emotional states, such as depression, which impact perceived rest.

Comparative studies have added nuance to these limitations, noting that while some brands like Garmin show high accuracy (approximately 89%) in distinguishing sleep from wakefulness, they struggle significantly with sleep stage classification. In one study of 62 healthy adults, Garmin received a score of approximately 0.21 on a 0 to 1 scale for classifying light, deep, and REM sleep, the lowest among compared devices. Experts emphasize that wrist-based hardware cannot directly measure the brain activity used in PSG, limiting precision in phase analysis.

Experts warn that relying solely on these metrics may provide a false sense of security, potentially delaying medical diagnoses. Medical professionals advise patients to prioritize personal well-being and physical sensations over digital statistics.