Gizmos Topic of the Week

How do smartbands track sleep?

It may be a smartwatch or a smartband. It may be cheap or really expensive. Whether it comes from design labs in Shenzhen or Cupertino, one thing is certain – it claims to track your sleep. Bad sleep has been linked with increased risk of heart attack, so this one matters: Do smartbands that track sleep quality work, and if so – how?

The science behind sleep tracking

Doctors use the electroencephalogram (EEG) to measure patients’ sleep, which works by monitoring the electrical activity of our brain. The EEG detects four sleep phases:

  • Awake – this is always the first step of going to sleep.
  • Light sleep – where memory consolidation takes place.
  • Deep sleep – the most helpful part of sleep for our body.
  • REM sleep – where we dream most vividly.

These sleep phases come in cycles: light sleep → deep sleep → REM sleep and all over again. Later during the night, sleep cycles may not include deep sleep.

The sensors that help smartbands track sleep

Unlike the EEG, smartbands track sleep without measuring brain activity. Instead, they rely on their heart rate and motion sensors to guesstimate our sleep patterns. Although this method is not 100% accurate, several scientists have shown that it is pretty good. Keeping in mind just how little data about the brain wrist wearables have access too, their performance is almost scary good!

How do wearables report sleep quality?

In general, sleep quality reports are pretty similar between devices. More expensive smartwatches usually report on REM sleep, which cheaper devices like the Xiaomi Mi Bands don’t. Most devices calculate a sleep quality score, although few actually describe how that’s calculated.

My smartbands track sleep. How can I use the data?

This is a bit of a gray area. Most sleep tracking apps imply that the target is to maximize deep sleep. Deep sleep is important indeed, but that doesn’t mean that the other sleep phases have no use. The way we sleep has evolved over million of years. For most of us, this means that our brain allocates the time it has to rest efficiently. What could we do to help it? Sleep more. And since even the cheapest smartband is very capable of tracking when we go to bed and when we wake up, all of us can use this simple metric to make sure we get enough sleep. In this era, when we can track almost all aspects of ourselves, the easiest solutions still work best.

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