How Does Your Smartwatch Measure Sleep?

Your smartwatch is an extension of your smartphone and can track your activities throughout the day. It can also monitor your sleep activity at night, such as how long you slept and how deeply. In this blog, you’ll learn more about the following topics:

• Why measure sleep?
• Monitoring sleep with your smartwatch
• What sleep information does a smartwatch measure?
• How does your smartwatch know you’re sleeping?
• How does the motion sensor work?
• How does the heart rate sensor work?
• Scoring sleep quality?
• How reliable is sleep tracking with your smartwatch?
• 3 smartwatches that monitor sleep

Why Measure Sleep?

Various sensors are now accessible and affordable for use with your smartphone and/or wearables, making it possible to monitor your sleep more effectively. You use the sleep monitor to better understand yourself in terms of sleep.

You might notice patterns, such as how eating too much or exercising intensely before bed affects your sleep quality. Based on these patterns, you can adjust your lifestyle to get the most out of yourself.

It’s also important to note that you shouldn’t compare your sleep quality to others, as personal factors like age, weight, height, and lifestyle significantly influence it.

Monitoring Sleep with Your Smartwatch

Getting enough sleep at night is essential for our bodies, as it allows us to recover from the day and process information in our brains. Sleep also recharges us for the next day. A lack of sleep can lead to fatigue, stress, and even permanent brain damage. If you want control over your sleep habits, a smartwatch with a sleep monitor is a great tool.

Ensure the following are in place when measuring your sleep:

• Keep your smartwatch on your wrist while sleeping
• Don’t wear it too tight or too loose on your wrist
• Keep the heart rate sensor active during sleep
• Keep the motion sensor active during sleep

What Sleep Information Does a Smartwatch Measure?

To assess your night’s sleep quality, your smartwatch needs data, collected through advanced built-in sensors. Your smartwatch measures the following sleep information:

• Total sleep hours
• Movement during sleep
• Sleep quality
• Light sleep (in minutes): The transition between being awake and asleep, where your eye movements slow and muscles relax
• Deep sleep (in minutes): A transition phase of about 30 minutes between light and deep sleep, where you rest
• REM sleep (in minutes): During your deepest sleep (REM), you may dream, and your body processes thoughts and emotions

How Does Your Smartwatch Know You’re Sleeping?

Your smartwatch is clever, but how clever is it? Clever enough to detect when you’re asleep. It uses the motion sensor and heart rate monitor to determine this.

How Does the Motion Sensor Work?

The motion sensor, also known as an accelerometer or acceleration meter, tracks your movements—not just arm or hand movements but also daily steps and calorie burn. During sleep, it measures how much you move. Your smartwatch combines these results with heart rate data (if both sensors are present) to score your sleep quality.

How Does the Heart Rate Sensor Work?

Besides being a key indicator of your health and exertion level, your heart rate helps measure sleep. Your smartwatch uses a green LED light for this. Have you noticed a green light on the underside of your smartwatch? That’s likely it emitting signals to measure your heart rate.

The green lights emit light, and the amount reflected depends on the blood volume under your skin. Blood flow varies with your heart rate, which changes with your activity level.

During an intense workout, more blood flows as your heart rate rises, reflecting more light to your smartwatch, indicating a higher heart rate. During sleep, the opposite occurs: your heart rate drops, reflecting less light, so your smartwatch knows you’re asleep.

Scoring Sleep Quality

Your smartwatch scores your sleep quality by combining data from the motion sensor and heart rate sensor. The sleep score indicates how well you slept.

This score, ranging from 0 to 100, is based on your sleep quality, personal data, and daily habits. Age, weight, and lifestyle all affect your sleep score. Each operating system has its own scoring criteria. Sleep scores can be categorised as:

Excellent: 90 – 100
Good: 80 – 89
Okay: 60 – 79
Poor: below 60

How Reliable Is Sleep Tracking with Your Smartwatch?

Your smartwatch tracks sleep using a motion sensor and a heart rate sensor. Some use only a motion sensor, which is less accurate. For instance, if you lie still for a long time, it might think you’re sleeping, potentially overstating your total sleep time.

A smartwatch with both a motion sensor and heart rate sensor is more accurate. It measures light, deep, and REM sleep with the heart rate sensor and detects wakeful moments more precisely due to rising heart rates.

However, don’t treat smartwatch sleep tracking as a medical diagnosis. It’s an indication of your sleep cycle. If you struggle to fall asleep or wake frequently, consult an expert who can measure brain activity during sleep.

3 Smartwatches That Monitor Sleep

The Garmin Venu 2 offers advanced sleep monitoring with a sleep score based on motion and heart rate sensors. It also features the ‘Garmin Body Battery’, which tracks your energy levels throughout the day. This connects stress, recovery, sleep, and physical activity into a simple score (0-100), where a higher number means more energy. The Venu 2 also includes other activity tracking and smartwatch features, justifying its price of £354.00.

The Galaxy Watch 4 measures sleep using motion data. Without a heart rate sensor, it’s less accurate than the Venu 2 or Bip 3 Pro. However, it offers many other smartwatch capabilities. The Galaxy Watch 4 is available from £139.00.

The Amazfit Bip 3 Pro tracks sleep with both a motion sensor and heart rate sensor, monitoring light, deep, and REM sleep. It records sleep duration, when you were in light or deep sleep, and how long you were awake. It also monitors sleep breathing quality. The Amazfit Bip 3 Pro is a budget-friendly option, available from £59.95.

Frequently Asked Questions

Is sleep tracking with your smartwatch reliable?

Your smartwatch provides a general estimate of your sleep cycle. For persistent sleep issues, it’s better to see an expert.

Why should I measure my sleep?

To better understand your sleep patterns. For example, if you notice short deep sleep at night, you can seek solutions.

How does a smartwatch know when you’re sleeping?

This depends on your smartwatch. One with only a motion sensor detects sleep when you’re still, though this is less accurate. A smartwatch with both a motion sensor and heart rate sensor knows you’re asleep when your heart rate drops and movement is minimal.

Which straps are comfortable for sleeping?

Our nylon straps, made from soft woven nylon, are ideal for sleeping, offering optimal comfort.