How Sleep Tracking Apps and Wearables Work — and How to Read Your Sleep Score

Sleep tracking apps and wearables measure how long and how well you sleep each night. They use sensors in your phone or watch — primarily motion sensors and heart rate monitors — to estimate when you fell asleep, when you woke up, and how much time you spent in different stages of sleep.

Common sleep stages you will see on apps include Light sleep (the stage from which you wake most readily), Deep sleep (the most restorative stage, important for physical recovery), and REM sleep (when most dreaming happens, important for memory and mood). Most adults need seven to nine hours of total sleep, including reasonable amounts of all three stages.

Popular sleep-tracking options include Fitbit (which has one of the most detailed sleep reports), Apple Watch with the Health app, Samsung Galaxy Watch, Oura Ring, and phone-only apps like Sleep Cycle or Google Fit.

A "sleep score" is a number — usually out of 100 — that rates how well you slept based on total duration, time in each stage, and how restless you were. A score in the 70s or above is generally considered good. Scores in the 50s and 60s often indicate insufficient sleep or frequent waking.

These trackers are not medical-grade devices and are not as accurate as a formal sleep study (called a polysomnography) done in a clinic. But they are good enough to reveal patterns — like consistently poor sleep on nights you eat late, or how much caffeine in the afternoon affects your nighttime rest.

Quick Tip: Charge your wearable in the late evening so it is fully charged before you go to bed. A dead battery overnight means no data.

Important disclaimer: This guide is for informational purposes only. Sleep tracking apps are wellness tools, not medical devices. If you suspect you have a sleep disorder such as sleep apnea, please consult a licensed healthcare provider for a proper evaluation.