OyasooHow accurate is sleep tracking with just your phone?
Accurate enough to answer the questions most people have, as long as you know which questions those are. A phone is good at telling when you slept and for how long. It’s poor at telling how deeply you slept, and it can be fooled in one specific way that’s worth understanding.
What sleep is actually measured with
In a sleep lab, sleep is measured with polysomnography: sensors on your head record brain activity, others track breathing, heart rate, eye and leg movements. That’s how sleep stages (light, deep and REM sleep) are defined in the first place. Everything else, from smartwatches to phone apps, estimates sleep from signals that tend to go along with it.
What a phone can sense
Depending on the app, a phone uses some of these:
- Phone use. When the screen is on and the phone is in use. You can’t use your phone while asleep, so use is strong evidence you’re awake.
- The phone’s movement. Picking it up, carrying it around, or, with the phone on the mattress, you turning over.
- Sound, for apps that record with the microphone: breathing, snoring, movement noise.
A phone can’t feel your pulse or measure brain activity. That’s the main difference from a watch or a ring, which add heart rate.
Where phone tracking does well
Reviews of consumer sleep trackers keep finding the same pattern: they’re fair to good at detecting sleep versus being up and about, and much weaker at sleep stages. Timing questions fall in the strong part:
- When did I fall asleep and wake up?
- How long did I sleep?
- Is that the same on weekdays and weekends?
- Is it getting later or shorter over the months?
For an app that works from phone use, the edges of the night are especially clear. The last time you put your phone down and the first time you pick it up are exact moments, not guesses.
Where it falls short
Lying awake still. This is the big one. If you lie in bed awake for an hour without touching your phone or moving much, nothing distinguishes that from sleep. Trackers in general tend to overestimate sleep for this reason, and more so for people who sleep badly. An app that only sees your phone will count that hour as sleep.
Sleep stages. Without brain activity or at least heart rate, any “deep sleep” figure from a phone alone is an educated guess. Treat it as entertainment, not information.
Shared beds. Apps that use the mattress for movement also pick up a partner or a pet.
How to use the numbers
Watch trends, not single nights. One night can be off by a fair margin; the average over a few weeks is far more reliable. Short nights every Sunday, or bedtimes drifting later, show up clearly even when individual nights are a bit rough.
Correct nights you know are wrong. If you remember lying awake from 04:00 to 05:30, fix the night. A good app learns from that.
Be wary of precision you can’t check. “7 h 12 m of sleep, 1 h 46 m deep” sounds exact, but only the first part is something a phone can reasonably estimate.
The honest summary
For most people, a phone-based tracker gives a reliable picture of when and how long they sleep, which is what matters for questions like whether they’re getting enough. It’s not a medical device and doesn’t diagnose anything. If you suspect insomnia, sleep apnea or another sleep problem, a doctor can arrange proper tests, and your tracked nights can be a helpful start to that conversation.
Oyasoo shows how sure it is about each night and lets you correct any night in a few taps, for exactly these reasons.