Health and Wellness

What Sleep Sensors Can and Can’t Tell You About Your Sleep

The amount and quality of your sleep have a huge impact on your waking life. For many years, data on how well (or not) you sleep was only obtainable via in-depth testing in a sleep clinic. More recently, technology has produced a range of sleep tracking devices that can provide you with personal sleep data outside of a sleep lab. Sleep trackers or sleep sensors fall under the following four basic categories.


Wearable trackers are most often worn around your wrist. Another type of wearable is sleep-tracking headgear. A sleep sensor on the forehead provides more accurate data on blood oxygen saturation and heart rate because of the proximity of the supraorbital artery.

Under the Sheet

These sleep trackers consist of thin pieces of fabric with embedded sensors that go underneath a bedsheet.


This type of sleep sensor has no contact with your body. The device is positioned a few feet from your bed and also takes in data about your bedroom environment.

Smartphone Apps

Mobile apps may require your phone to be very close to your body in order to collect accurate information.

What do Sleep Sensors Measure?

  • Sleep Metrics – As well as total time asleep, sleep quality, and body positioning, some trackers will estimate the time spent in each sleep stage. It’s even possible to compare your results with the typical time in each stage for people of your sex and age. Also, some sleep sensors come with a smart alarm designed to wake you at the optimal time in your sleep cycle.
  • Movement – Sensors can keep tabs on how often you get in and out of bed and your progression through each sleep stage. They can also assess the rise and fall of your chest as you breathe.
  • Heart Rate – Wrist devices can take your pulse with a high degree of accuracy. Smartphone sleep tracking apps employ a technique called optical heart rate monitoring. An undersheet tracker utilizes a method called ballistocardiography (BCG).
  • Noise – Noise sensors can detect and record night sounds to determine if your sleep is being disrupted by noise. Data can also tell you whether you snore or have breathing issues.
  • Temperature – Temperature sensors can tell you how hot or cold your bedroom is. Some trackers have thermometers that measure your sleeping body temperature.

How Accurate Are Sleep Sensors?

Sleep trackers can provide some interesting data on how well (or otherwise) you sleep. However, many of these products are relatively new, and long-term data on accuracy is lacking. Here are a couple of limitations to be aware of:

  • Trackers can’t tell the difference between being awake and motionless and being asleep. However, many devices allow you to state when you’re trying to go to sleep rather than just relaxing.
  • Sharing a bed may compromise data from any tracker that is not worn directly on the body.

The Bottom Line

A sleep tracker is an affordable and accessible means of getting initial data on your sleep health and quality. However, you may need a medical professional to get to the bottom of your sleep issues and possibly a referral to a sleep clinic.

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