Does your sleep tracker get it right? A Pittsburgh neuroscientist weighs in
A growing share of people wear a tracking device to bed, hoping it can tell them something about how they slept. andreswd/E+ Collection via Getty Images On a typical night, I go to bed wearing a tracking watch on one wrist and another type of tracker on the other wrist.
Sleep trackers are wearable devices, like smartwatches, that monitor sleep by measuring heart rate, movement, and skin temperature. They estimate how long you slept and sometimes which sleep stage you were in, such as light, deep, or REM sleep. These devices do not directly measure brain activity like medical-grade equipment does. Instead, they rely on algorithms that interpret patterns in heart rate variability and movement to guess sleep stages. For example, REM sleep, the stage associated with dreaming, has a distinct cardiovascular profile that trackers attempt to recognize. While these devices are convenient for daily use, their accuracy depends on the quality of their sensors and software, which can vary significantly between brands and models.
To test how well sleep trackers perform, researchers compare their results to polysomnography, the gold standard for sleep measurement. Polysomnography uses an electroencephalogram (EEG) to record brain waves, along with sensors for eye movements and muscle tone, providing a detailed picture of sleep stages. A 2025 meta-analysis of 24 studies involving nearly 800 participants found that wearables typically overestimate total sleep time by about 17 minutes per night compared to polysomnography. This represents an error of under 4% in an eight-hour night. The main reason for this discrepancy is that trackers often mistake quiet wakefulness—lying still without sleeping—for actual sleep. This issue is more pronounced for people with insomnia, who may spend long periods lying awake motionless.
Sleep trackers struggle to accurately identify specific sleep stages, such as light, deep, or REM sleep. A 2025 study of six wrist devices worn by 62 adults found only modest agreement with polysomnography when tracking sleep stages. The devices also showed significant gaps in measuring time awake after falling asleep and sleep efficiency. Researchers concluded that while better-performing watches could detect prolonged and significant changes in sleep architecture over time, their nightly estimates of sleep stages are noisy and unreliable. For instance, the deep-sleep number provided by a tracker is best interpreted as a rough estimate rather than a precise measurement.
Despite their limitations in tracking sleep stages, sleep trackers are relatively accurate at measuring total sleep duration. A 2023 study published in Proceedings of the National Academy of Sciences used Fitbits to track the sleep of over 600 first-year students at three universities, including Carnegie Mellon University. The study found that students sleeping six or fewer hours per night early in the semester had lower end-of-term grade-point averages compared to their previous semester, even after accounting for academic load and naps. This suggests that nightly sleep duration, which trackers measure reliably, is a useful metric for assessing sleep's impact on academic performance.
Sleep trackers can influence how people feel about their sleep, even if they don’t change the actual amount or quality of sleep. A 2023 randomized trial with 113 adults experiencing insomnia symptoms found that those who received feedback on their sleep data from a wearable, along with guidance on interpretation, reported milder insomnia symptoms than those who only received general sleep-hygiene advice. However, the measured sleep duration did not improve in the feedback group. Instead, the tracking seemed to reduce anxiety about sleep, as participants felt less troubled by their sleep issues. This aligns with the Pittsburgh Sleep Quality Index, a widely used questionnaire developed in 1989 by researchers at the University of Pittsburgh, which measures subjective sleep quality rather than objective sleep data.
For some people, sleep tracking can become a source of stress rather than a helpful tool. Clinicians refer to this phenomenon as orthosomnia, a term coined in 2017 to describe patients who lie awake worrying about their sleep scores. If checking a tracker’s results leads to increased anxiety or preoccupation with sleep, the device may do more harm than good. A 2026 trial involving 229 older adults in Japan found that participants who received monthly guidance on sleep habits and daytime activity, in addition to sleep reports, showed improvements in their insomnia scores over the first three months. However, those who only received sleep reports without guidance did not see improvements, highlighting the importance of using tracker data as a tool for action rather than a source of stress.
Experts recommend using sleep trackers as a trend-monitoring tool rather than relying on them for precise nightly data. For example, tracking sleep over weeks or months can help identify patterns or significant changes in sleep duration or efficiency. It’s also important to remember that device models and algorithms evolve rapidly, so a study’s findings about a tracker’s accuracy may not apply to newer versions. The author of the article, a neuroscientist at Carnegie Mellon University, compares reading sleep tracker data to checking a weather forecast: useful for identifying trends but not for predicting exact conditions. If tracking increases anxiety, it may be worth reconsidering its use or seeking guidance from a healthcare professional.
