A sleep tracker is reasonably good at telling whether you are asleep, but much less good at telling which sleep stage you are in — and those stages are what the app shows biggest. People who let the numbers steer them can end up sleeping worse; sleep researchers call this orthosomnia. The most reliable measure remains how you feel in the morning, several weeks in a row.
A ring or watch doesn't look inside your head. It infers your sleep from movement, heart rate and sometimes temperature, and calculates a sleep stage from that. A sleep lab measures brain activity itself. That is the difference between an estimate and a measurement.
Compared with sleep-lab measurements, consumer devices recognised sleep well, but moments of wakefulness much less well, and their sleep-stage scoring was mixed. On disturbed nights — exactly the nights you want to know about — they did worse. Newer devices have improved, but the principle remains the same.
In 2017, sleep researchers described patients who became so fixated on their sleep score that their sleep deteriorated. They called it orthosomnia, after orthorexia: an unhealthy obsession with healthy living.
A familiar pattern: staying in bed longer to push the score up. But lying in bed longer than you sleep makes sleep lighter and more restless — which is why sleep therapy often prescribes the opposite. Go to sleep to hit a number, and you no longer sleep to rest.
Look at weeks, not nights. One poor score says nothing; a trend over a month might.
Use it for what it measures well: when you go to bed, how regular that is, and how long you spend in bed. Take the percentages of deep and REM sleep with a large pinch of salt.
And if you notice the score makes you restless: put it away for two weeks and pay attention to how you feel. That isn't failure; it is the researchers' own conclusion.
Whether a bed suits you can't be read from one night with a ring. How you lie, how often you turn, whether you wake up stiff and how you feel at ten in the morning — that says more.
With an overnight stay at SleepSpa we offer a sleep measurement, but as an aid to the conversation, not as a number to choose a bed by. If you'd rather not measure, you sleep without. That is a perfectly good way to be here.
Reasonably reliable for whether you slept and for how long, less so for time awake and least for sleep-stage scoring. It becomes less accurate on disturbed nights. Use it for trends over weeks, not to judge a single night.
A term from sleep medicine (2017) for people whose sleep worsens because they become fixated on their sleep data — for example by staying in bed longer to get a better score.
At most over a period of weeks, and even then with a lot of noise. How you lie and how you feel in the morning say more than the difference in sleep score between two nights.