20 Sensors Present in Smartwatch: How They Work, Use Case, and More?

Sensors Present in Smartwatch

Smartwatch has evolved over the years, earlier we use to get heart rate monitoring but these days, we can use the smartwatch to monitor stress, sleep, calorie count, and even body mass.

Now, to process all data at the same time, smartwatch manufacturers use all kinds of sensors and in total, if smartwatch brands want then they can add 20 sensors.

So let’s take a look at each sensor and its use case, so you can get some idea of what’s that what does green light behind the smartwatch do.

Sensors Present in Smartwatch

You may have heard that Apple Watch saved a person’s life by alerting the heart condition and to monitor that, Apple has been using the ECG sensor which is the key selling point of the Apple Watch.

We don’t see, an ECG sensor in a budget smartwatch because the sensor is a bit expensive.

So as you can see, wearables have come a long way from just fitness tracking to saving a life.

By the way, as I have said, you won’t get all the 20 sensors in a single smartwatch, it will depend on the price of the smartwatch and whether the government allows to use of certain sensors on the smartwatch or not.

In short, just like everything else, double-check the product page before you order a smartwatch.

1. ECG sensor

ECG Sensor on Smartwatch

An electrocardiogram (ECG) is a simple test that can be used to check your heart’s rhythm and electrical activity.

Earlier we use to visit the hospital to test the ECG but when Apple started giving the ECG sensor in Apple Watch, a normal person at home with one touch can check heart condition.

So if you’re having problems like chest pain, or coronary artery disease, in this case, ECG can give you the idea of whether you have any problem in your heart or not.

Now if you’re getting an ECG sensor in Rs 10000 or even Rs 5000 smartwatch then double check the quality of the ECG sensor because sometime, to sell more smartwatches, some brands can add cheap sensors.

When you test ECG on a smartwatch, the closed-circuit allows your watch to record all the electrical impulses that make your heartbeat.

The last question would be, is ECG on Smartwatch reliable?

Now, this depends on which smartwatch you’re using it. Talking about Apple, they have FDA clearance and they have claimed 99.99% accuracy.

2. Gyroscope

Gyroscope on Smartwatch

You may have used the Gyroscope in games like PUBG or even COD Mobile and yes, the same sensor is used on smartwatches too.

The Gyroscope tracks body movements, whether you setting, sleeping, or even running, the Gyroscope collects all the data.

Now, you may have used the Raise to Wake feature on a smartwatch, the same feature is made possible because of the Gyroscope sensor.

By the way, the smartwatch also uses the Gyroscope for sleep tracking.

3. Accelerometer

Accelerometer Sensor in Smartwatch

No matter which Smartwatch you’re using, it will have an Accelerometer sensor because it helps to track the movements of your body by counting the number of steps you have taken throughout a period.

So when a smartwatch tells how that, you have taken 5000 steps in 24 hours means, the Accelerometer sensor working in the background to provide that data.

The Accelerometer sensor is also used to track your sleep too, while you’re in sleep, the sensor tracks your movements and fingers out, and how many hours you have slept.

Just like ECG, a budget smartwatch doesn’t use a good quality Accelerometer sensor, so make sure your read review to know whether the watch you’re buying has a good Accelerometer sensor or not.

According to research, sleep trackers to are only found to be accurate 78% of the time. And when it comes to estimating how long it took for people to fall asleep, the accuracy dropped to a mere 38%.

4. Oximetry Sensor

how spo2 sensor works in smartwatch Image02

We all have used this sensor during pandemics because it tells you the Oxygen concentration in your blood. You might Oximetry Sensor as SpO2.

When you measure the SpO2 on a smartwatch, it projects LED lights into the skin to measure oxygen levels, the difference between injected light and reflected light is the final result of SpO2 in blood cells.

The smartwatches use photoplethysmography (PPG) sensors to measure the SpO2 percentage as well as the Heart-Rate.

How SPO2 Sesnor works Image01

According to WHO, a patient with oxygen saturation of 94% or lower needs quick medical attention. And if less than 90%, it’s a clinical emergency.

So what I’m saying is, if your smartwatch is showing SpO2 levels of 90% and you don’t have any symptoms which I mention then there is a chance that, the smartwatch you’re using is unreliable, you better get an oximeter.

I have already written, How SpO2 sensor on works Smartwatch, so if you wanted to know whether the SpO2 sensor on a smartwatch is accurate or not then do read that article.

5. Compass or Magnetometer

How Accurate is Smartwatch GPS?

The Magnetometer is just another name for the Compass sensor, it works with GPS to provide your location.

Now, we don’t get Compas sensors on budget smartwatches because if the brand provides all the sensors then the watch won’t remain in the budget segment but some of the premium smartwatches do provide this sensor to provide an accurate location.

6. Body Temperature Sensor

Body Temperature Sensor

A body temperature sensor on a smartwatch is used to measure your skin temperature. The sensor detects the change in your body temperature this way you can determine whether you have a fever or not.

You may have seen this sensor during the Pandemic, someone from the medical field may have used this sensor on your forehead to see your body temperature

These sensors can also help detect menstrual cycles as well.

Because of the Pandemic, we have used this sensor a lot and that’s the reason why we’re seeing Body Temperature Sensor in budget smartwatches too.

7. Barometric Pressure Sensor

Barometric Pressure Sensor on Smartwatch

A barometric pressure sensor is used to detect atmospheric pressure. For example, changes in the pressure caused by weather patterns, the altitude, and air pressure of the current location and records the measurement data of the current day in a waveform graph.

Outdoor watches will continually monitor barometric pressure to determine which mode is most appropriate at any given time.

It can also measure whether the SpO2 is increasing or decreasing when you move to the higher side.

In short, it’s a weather application on your Smartwatch.

8. Heart Rate Monitor

Heart Rate Sensor on Smartwatch
Image: Cavosmart

One of the key selling points of a smartwatch is Heart Rate Monitoring, it helps detect pulse rate. Most smartwatch brands use photoplethysmography (PGP) sensors for the same.

The photoplethysmography sensor measures the SpO2 percentage as well as the Heart-Rate.

We all have seen that green light on the back side of a smartwatch, the same green light is injected into your skin, and the greenlight detects the changes in the blood by measuring the amount of light reflected.

Most budget smartwatch uses the PPG sensor while some premium smartwatches use the ECG sensor and yes, ECG provides more accurate results compared to PPG.

9. Ambient Light Sensor

Ambient Light Sensor on Smartwatch

Just like how smartphones automatically brighten the screen, the same way, the smartwatch also has the feature to adjust the brightness according to the lights, the smartwatch uses the Ambient Light Sensor to do all this work.

For example, if you’re under good lighting then the smartwatch will automatically increase the screen brightness while under low light, it will decrease the screen brightness and all these tasks are done by Ambient Light Sensor.

10. Altimeter Sensor

Altimeter Sensor on Smartwatch

An altimeter sensor measures altitude location’s distance above sea level. For example, climbing, walking on stairs, running, or even normal walking.

The Altimeter Sensor works in the background when you’re exercising, it improves the calorie burn rate.

11. Bioimpedance sensor

Bioimpedance sensor on Smartwatch
Image: nature.com/srep

If you’re wearing any smartwatch and at the same time, you sitting on a chair for more than an hour then you will get a notification on the smartwatch that, you’re inactive for while, get up and take walk. So feature works because of the Bioimpedance sensor, it can be also used for water reminders too.

Now, here comes the technical definition…

A bioimpedance sensor measures the resistance that your skin is offering to a small amount of electricity. The battery charger electrodes in the fitness tracker deliver a very small amount of current to measure sleep, heart rate, respiration rate, water level, and more.

For those who don’t know, the Samsung Galaxy Watch 4 comes with a Bioimpedance sensor that uses for blood pressure, irregular heart rhythm (AFib), blood oxygen, and body composition too.

12. Electrodermal Activity Sensor (EDA)

Electrodermal Activity Sensor on Smartwatch

The Electrodermal Activity Sensor (EDA) helps you measure stress by combining the data from ECG, Skin Temperature, and heart rate sensors. Some of the smartwatches also use sleep data to provide accurate streel levels.

We’re also seeing the Stress monitoring option in budget smartwatches which is fake because they ask five or six questions and after they provide the stress levels which is useless whereas brands like Fitbit use the Electrodermal Activity Sensor (EDA) sensor.

13. GPS Sensor in Smartwatch

How Accurate is Smartwatch GPS?

The Global Positioning System (GPS) uses Satellites from orbit approximately 21,000km above the earth’s surface. Most smartwatch receives singles from 4 different satellite which moves around the earth twice a day.

When the smartwatch receives data from the satellite, it then uses the algorithm which is made by the smartwatch brand and calculates all the data and provides as accurate data as it can.

Now, each brand uses a different kind of algorithm, so the data might be different on each smartwatch.

For example, Apple Watch will give you accurate data compared to a random smartwatch worth Rs 5000 because Apple had done R&D for the years and if they want they can spend more money but a new brand will take some time.

In the end, it depends on which brand’s Smartwatch you’re using it.

Also, if you want to know more about the GPS tracking on Smartwatch then I have written a detailed article on it, make sure you read it.

14. Orientation Sensor

Its basic sensor which is used by most smartwatches, tells you whether the smartwatch is in the right direction or not and if not then the sensor will start working and the screen will come back to the original position.

It’s the same way, how smartphone orientation works.

15. Proximity Sensor

A proximity Sensor is used by the smartwatch to determine whether you’re using the smartwatch or not, if you’re not using it then the watch will go into sleep mode.

Also, if the watch has a calling feature then it will turn off the screen when you raise your hand toward the ears.

Again, the same we have seen in smartphones too.

16. Pedometer Sensor

A pedometer sensor is used to count the footsteps. Almost all the smartwatches whether priced at Rs 1000 or Rs 10000, will have a pedometer sensor.

When you walk the 5000 or 1000 footsteps then you will get a notification from the watch that you have completed today’s goal.

17. Calorie Counter

This is what you’re thinking, with the help of the Accelerometer sensor, it provides the burn Calorie count on the smartwatch screen.

You can also see all the data on the smartwatch application, each brand uses different apps, so use one accordingly.

18. UV Sensor

UV Sensor on Smartwatch
Image: techentice.com

The UV Sensor is used to measure whether the outdoor sunlight is harmful or not. Now, we don’t have many smartwatches that offer UV sensors but some are there.

19. Gesture Sensor

You may have used the Gestures on a smartwatch, for example, swiping down can bring a notification bar or you can take or reject a call with a single tap. All these Gestures by the smartwatch brand are added using the Gesture Sensor.

20. Skin Conductance Sensor

As of now, we don’t have many smartwatches that feature the Skin Conductance Sensor, maybe in the future but as of now, it’s not a widely available sensor on smartwatches.

Basically, the Skin Conductance Sensor helps calculate something called galvanic skin response, it interacts with the sweat glands as electrodes in your watch are quite sensitive.


Yes, that was it, these are the 20 sensors used on smartwatches, if any new sensors come in then I will add them right here.

Now, do let me know, out of 20, how many sensors does your smartwatch has?

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