Smartwatches are a great invention that happened just at a time when wearing watches around the wrist is becoming a redundant activity. Since the advent of smartphones, nobody was checking the timepiece on their wrist to know the time anymore, so to avoid extinction, watches needed to offer something more than telling the time. 

The only thing smartwatches have in common with traditional watches is the fact that they are worn around the wrist. The functionality of smartwatches is diverse and an important role they play in today’s lifestyle is tracking sleep patterns. 

How does a smartwatch know when you sleep?

But how does a smartwatch know when you are asleep? With most technologies, adoption is largely based on functionality and popularity, not very many people are interested in the nitty-gritty of how these things work and I get it. 

Our life today is immersed in so many devices and appliances that it is impractical to be fixated on something that works, as long as it gets the job done. However, there are still some people who love to uncover these things, so if you are interested in knowing how a smartwatch knows when you sleep, you have come to the right place. 

Measurement of body movement patterns 

Most of the smartwatches today use the measurement of body movement patterns to determine whether you are sleeping or not. Because they are worn on the wrist, they are able to tell when your body is saying still from when you are engaged in regular day-to-day activity. After an extended period of uninterrupted stillness or minimum and subtle interruptions, the device automatically assumes that your body has gone into a sleeping phase.

Motion sensor 

The part of the smartwatch that is responsible for this measurement is a sensor called an accelerometer or most commonly pedometer. This motion sensor plays a dual role as it is the same component of the device that is responsible for monitoring and measuring the number of steps you take daily and responsible for detecting overall physical activity. 

In some other smartwatches, in addition to the generic motion sensor, there are specific sensors that detect the slightest movement in the wrist.  These sensors are capable of detecting changes in the direction and manner of wrist placement and this is a huge contributor to how a smartwatch knows when you sleep. 

As simple as this sounds, it is a proven technique for detecting sleeping patterns and the field is described as actigraphy. An actigrapher is the original device that accelerometer-based smartwatches are fashioned after. The movement data collected by the accelerometer in smartwatches are interpreted to give an indication of the sleep pattern of the wearer of the device. 

Monitoring of heart rate 

In addition to measuring wrist and body movement and collecting important data related to these parameters, some smartwatches are also equipped with the capacity to measure and monitor the heart rate. This is the most recent innovation in the field of sleep-tracking devices and it is inching close to the approach utilized in standard clinical procedures. This addition to the smartwatches enables them to monitor the beats per minute (bpm) of the heart during sleep giving an insight into the stage of sleep per time. The heart rate is expected to drop during sleep and the deeper into the sleep cycle, the lower the beats per minute data recorded is expected to be.

Heart rate Sensors 

Most smartwatches today are equipped with an optical heart rate sensor. In addition to being the component that calculates the beats per minute, it monitors blood flow from the heart through the arteries that pass through the wrist where the watch is worn. More precisely, it monitors the speed at which blood is flowing from the heart through the arteries on the wrist. 

Measurement of Sleep in Clinical Research 

Sleep quality and its measurement is an established field of clinical research largely due to the importance of sleep to the wellbeing and optimal functioning of the human body. Although actigraphy is employed by clinical scientists, a more superior approach is often preferred to accurately determine or sleep quality of a patient. One of the most common approaches by scientists is polysomnography which is a comprehensive testing procedure employed in the diagnosis of sleep disorders and serious medical examinations. 

In this case, polysomnography combines a lot of factors in the measurement procedure and collects data from different body parts and activities. This includes the organ responsible for sleeping and that gives the most accurate indication of sleeping pattern or a lack thereof, the brain. Several sensors are attached to different body parts including the scalp, the chest, the wrist, and other parts. 

These sensors measure the brain waves, heartbeat, movement of the eyes, body movements, and breathing patterns. As you can probably imagine there are a lot of wires and cables involved in this process and it is quite complicated but it is not invasive. You certainly do not need this if you are merely looking to live a balanced lifestyle, pay attention to your body and stay healthy. 

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Although the movement is arguably not the most accurate measurement of sleep and additional data is required to get an in-depth interpretation of the sleep cycle and the sleep quality, smartwatches are a brilliant invention. Most people do not need the comprehensive sleep measuring devices because it is reserved for serious sleep disorders. So, if your goal is to get a decent amount of sleep around the recommended 7 to 8 hours for a normal adult then, smartwatches will work just fine. They give a pretty good indication of sleep quality that is adequate for the average person. 

It is also important to remember the smartwatches do not merely track sleep, they collect data that can be analyzed to give an insight into your sleep cycle and the overall quality of sleep. These are smart devices that can interpret collected data to offer suggestions and lifestyle improvements that can guarantee improved sleep health.