Half of us wear one

Nearly half of American adults have tried a sleep tracker, chasing numbers on hours slept and schedule consistency. New research says the devices miss a big piece of the picture.

The numbers and the feeling split

Researchers pooled data from more than 2,000 people and found tracker readings often had little to do with how rested those people said they felt.

“your sleep tracker might tell you that you slept great, even if you wake up feeling awful”

They explain almost nothing

Wearable measurements accounted for just 2.5 to 16% of the differences in how people rated their sleep quality. The other 84 to 98% came from somewhere the device never saw.

Worst for the people who need it

Against clinical polysomnography, Fitbit agreed with the lab in 82.4% of healthy sleepers. Among people with insomnia, that fell to 39.4%. Older adults and people with other conditions fared poorly too.

Lying still looks like sleeping

Trackers likely read motionless wakefulness as sleep, so the hours spent staring at the ceiling vanish. One study found devices overstated sleep time by 30 minutes and sleep efficiency by 8%.

“device measurements may provide misleading information that could delay appropriate clinical intervention”

Keep it, add a diary

The gap matters most when a tracker reassures someone with real insomnia and keeps them from a doctor. Pair the device with notes on how rested you feel and whether you remember lying awake.