How do Smartwatches Work? What do Smartwatches measure, and How? – An Ultimate Guide

Smartwatches are now embraced by many, given their high-tech functionality and convenience. They have indeed made life much more comfortable. But have you ever wondered how smartwatches work? If you own one, you can tell its usefulness based on all the various aspects and parameters it measures.

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The devices tell the time and utilize the latest technologies to help measure your heart rate, track various activities, measure blood oxygen levels, measure temperature, and so much more. They are also your ultimate fitness companions and could help you in health-related matters. In this article, you will learn more about that and how smartwatches do their magic.

How Does A Smartwatch Work?

Smartwatches are digital watches that do more than tell the time. They contain small computers that run on their own operating systems. You will need a smartphone to explore the full potential of your smartwatch. From the smartphone, you will be required to download the app for the smartwatch-like Watch or Android wear for Apple and Android phones, respectively.

Once you fully install the app, connect your Bluetooth with the watch, and you can now synchronize the two devices. With this done, you can easily view notifications on your watch, view calendar appointments, read messages or emails, and even make and receive phone calls.

Another essential function of smartwatches is that they measure daily activities as well as exercises. Many of them come with a built-in heart rate sensor and GPS that come in handy to measure your daily activities. These include sleep patterns, counting steps, calories burned, and so on. With the GPS, you can also tell the distance covered while cycling or running.

On top of that, smartwatches come with a wide range of applications. You can also install other third-party apps for the best experience. The popular apps include Whatsapp, Spotify, Buienradar, Apple, and NS Reisplanner.

What do Smartwatches measure, and How

Some of these apps offer you incredible convenience, such as when you go shopping without your wallet or phone or inform you beforehand how the weather will be. Now let us look at the various parameters smartwatches measure and how.

1. How do Smartwatches measure Heart Rate?

Some smartwatches come equipped with heart rate tracking features to measure the variations of your heart rate. These watches employ the heart rate monitor technology (HRM) to measure your heart rate. Heart rate measurement is done by scanning the blood flowing near your wrist through illumination with LEDs.

You will notice the color green on most bands. The color is well selected as it is absorbed well by the red blood. The optical sensors can therefore gauge the blood flow and, ultimately, the heart rate more accurately.

The heart rate variability HRV, which is the interval between heartbeats, is also used by some smartwatches to determine your heart rate. Have a peek at best smartwatches with heart rate monitor for better understanding.

2. How do Smartwatches measure Blood Pressure?

High blood pressure could be the cause of heart attack, stroke, and dementia. Keeping tabs on your blood pressure is therefore vital. Some smartwatches employ the Pulse Transit Time technology to measure your blood pressure. This technology uses two sensors; the optical heart rate monitor, and the electrocardiogram in your smartwatch.

The sensors help obtain data to calculate the Pulse Transit Time; that is, the time it takes for a pulse to travel from your heart to the wrist. Generally, the pulse will travel faster if the blood pressure is high. If the blood pressure is lower, the pulse will travel slower.

3. How do Smartwatches measure Blood Oxygen Level?

Measuring the blood oxygen levels is one of the latest technology metrics. Measuring one’s blood oxygen may seem a little complicated. Still, this data is beneficial in revealing some conditions such as sleep apnea, and could even help you recover from other conditions.

Pulse ox is now commonly featuring in the specifications of many smartwatches and fitness devices. It is also on the must-have list of many looking to buy an ideal smartwatch. But how does it work?

In medical terms, pulse oximeters are devices used to measure oxygen or oxygen saturation in the blood. Traditionally, this technology was in the form of a clip-on device placed on a finger, toe, or ear lobe.

The optical SpO2 sensors make use of red and infrared light sensors that detect the blood oxygen levels. They are designed to sense any changes in the oxygen levels by the color of your blood.

Moreover, they can measure the oxygen volume through how the light passes through the finger delivering data to the screen. This information displayed will tell you the oxygen percentage in your blood.

If your oxygen percentage saturation is above 95%, then that is considered an average reading. If you score 92% or less, you need to undergo further investigation to indicate an undetected health issue.

The measurement is crucial as you can use it to check whether one needs any assistance with their breathing, whether they are experiencing any breathing problems while asleep, or their ability to handle the intensive physical activities.

Furthermore, the sleep apnea condition is what makes the SpO2 sensor worthwhile.

4. How Smartwatches measure Stress?

The stress level feature is found on many smartwatch devices and is used to determine one’s current stress level. The stress level is based on the heart rate variations. The stress level feature works in conjunction with the heart rate monitor, whose data determine the intervals between each heartbeat.

The variations in the length of time between each heartbeat are generally regulated by the autonomic nervous system of your body. The watch records higher stress levels if the variability between beats is less. An increase in variability indicates less stress.

5. How do Smartwatches measure Sleep?

Sleep tracking has become increasingly popular in the manufacture of smartwatches. But how do they do it?

Smartwatches are designed to track sleep with great accuracy. They are designed to track when you fall asleep, your sleep quality, the amount of time you sleep, how much time you spent in each sleeping stage, the quality of your sleep environment, and other sleep-related health metrics.

The watches can tell you are asleep through your body movements. Generally, we are almost entirely still while asleep as compared to when we are awake. Body movement is, therefore, one useful indicator that smartwatches use to tell the time we sleep.

The body movement is measured by either accelerometry or actigraphy, depending on the smartwatch model. Wearable sleep trackers mostly use an actigraph sensor, whereas the smartwatches rely on the accelerometer to measure body movement and assess whether you are asleep.

Besides body movement, the smartwatches measure other environmental and personal factors to determine whether you are asleep or not.

For instance, they come with a built-in microphone to capture noise from your body or the room. The presence or absence of noise can determine if you are asleep and provide insight into the sleep quality.

Moreover, the microphone measures your respiration, and this detects any snoring. The watch may also suggest the best sleeping environment and what interferes with your sleep quality if any. Visit this review post about best smartwatch to track sleep. The watches with a heart rate monitor can tell your heart rate variations, and this also helps to indicate whether you are asleep.

Generally, when you are asleep, your heart rate slows down and remains steady throughout your sleep duration, except for REM sleep. When awake and in REM sleep, the heart rate increases, as so do the variations.

6. How do Smartwatches measure Steps?

Smartwatches, especially the fitness trackers, will require their users to input their physiological details like height, gender, and weight to make better sense of any data it collects.

Moreover, this personalization makes it easy for the smartwatch to process the data it generates. There are several sensors that these smartwatches come with, but for measuring steps, the motion sensors are of great use to determine your body movements.

These smartwatches are designed to sense the body movements continuously on a 3-axis accelerometer. This data is recorded as long as the watch is worn and well powered up. Therefore, the tracker can trace whether the user is walking, standing still, or running fast.

The data is then stored in the watch, awaiting further processing. The processing will take place once the data is transferred to software associated with the watch on your smartphone.

And since the software is personalized with all your details, the data is run through a personalized algorithm. The movements are categorized into different activities to generate more information.

The information is then stored in your app under different headings. So, if you want to know the steps you took in a day, you can tap the app. The app has a wide range of other information, so you can also tell your pace, at what speed, and the calories burned.

7. How do Smartwatches measure Calories?

Again, this mostly applies to the fitness tracker smartwatches. Besides distance covered and step count, they can estimate the number of calories you have burned.

Generally, our bodies burn calories through digestion, physical activities, and when maintaining essential body functions. The smartwatches determine calories burned from your physical activities that are recorded on the same device.

They monitor a wide range of information, whether it is walking down to the shops, going for a run, and so on. They take information from other sensors such as accelerometer and use a different algorithm, which differs in different models to estimate the calories burned.

With these estimates, you can now decide what to drink, eat, or which workout works best.

8. How do Smartwatches measure Temperature?

Some smartwatches may come fitted with a thermostat feature for temperature measurement. This is aided by an electrodermal activity sensor (EDA) to measure your skin temperature.

If your skin feels chilled, hot, or clammy, the watch can tell the current temperature. The temperature measurement is also useful in stress detection.


Smartwatches are lifesavers and necessary investment. These devices come in handy in so many instances. And how they work has been a mystery to many. Constant testing of one’s blood pressure, heart rate, blood oxygen levels, and even stress levels, could be somewhat inconvenient for many. We can all agree that it is so much more comfortable with smartwatches. And now, you know how they do it.