How smartwatches & fitness bands measure heart rate

How smartwatches measure heart rate

Smart watch and fitness bracelets are very popular gadgets nowadays, they can do more than just show you an hour as they help us to track our fitness activities, heart rate and sleep monitoring. But when it comes to heart rate monitoring, one question always comes to my mind: how does the smartwatch measure heart rate? Or how the smartwatch works to measure heart rate.

So in this article, I’m going to share with you some information about how smartwatches and fitness bracelets measure heart rate.

So without further ado, let’s get started!

What heart rate is?

Simply put, a heart rate is a specific number of times your heart beats in a minute. It depends on what you are doing, whether you are resting it beats more slowly or whether you are exercising; it beats faster. As you get older, changes in the rate and regularity of your pulse may change and may signify heart disease or some other condition that needs to be treated.

How do smartwatches or fitness bands measure heart rate?

If you are using the smartwatch of a fitness band, you may have noticed the green light and the plethysmogram (PPG) sensor on the device. This green light and PPG sensor plays a vital role in heart rate measurement. Our red blood absorbs green light and reflects red light, which is why we see that most smartwatches or fitness bands have green LED lights on the back of the device.

When blood is flowing in the hand, the smartwatch or fitness bands will flash green LEDs hundreds of times per second, while the PPG sensor measures the number of heartbeats (heart rate) per minute.

Wondering how this PPG sensor works? Next, let’s understand how this PPG sensor works.

Photo plethysmography (PPG) is the process or technique to be used to detect the volume of blood flow in order to understand the change in heart rate through the skin. Traditionally, ECG (ECG) sensors have also been used to measure heart rate and detect rhythms, but ECG sensors are a bit bulky and cannot be used to detect heart rate when the body is moving. .

Principles of the photo plethysmogram (PPG)

As mentioned above, PPG uses low intensity infrared green (IR) light. When light passes through living tissue, it is absorbed by bones, skin pigment, and venous and arterial blood.

Light is absorbed more strongly by the blood than by the surrounding tissue, so the PPG sensor can detect changes in blood flow as changes in light intensity.

The voltage signal from PPG is proportional to the amount of blood that flows through the blood vessels. This method offers a higher level of accuracy, as they can detect even slight changes in blood volume.

How does this technology work?

According to, the smartwatches or fitness bands use four major components:

  • Optical emitter
  • Digital signal processor (DSP)
  • Accelerometer
  • Algorithms

Optical emitter

The optical emitter typically contains at least two LEDs that transmit light waves into the skin or wrist. Because of the vast differences in skin tone, thickness, and morphology associated with the diversity of consumers, most OHRMs use multiple wavelengths of light that variably interact with different levels of skin and tissue.

Digital signal processor (DSP)

When the light is transmitted into the wrist via the smartwatch, some lights are reflected back to the sensor, which contains the digital signal processor (DSP) that detects the light and converts those signals to another null that can be measured into meaningful data from the heart .


Accelerometers measure movement and input into the PPG algorithm along with DSP signals.


The algorithm processes exercise tolerant heart rate data such as VO2, calories burned, RR interval, changes in heart rate, blood metabolism values ​​and blood oxygen values ​​from DSPs and accelerometers.

Is your Smartwatches accurate for heart rate?

The smartwatches or fitness bands are most likely not accurate when compared to professional medical devices. But they’ll get almost closer to measuring your heart rate, not exactly. It is therefore recommended that you do not rely entirely on this type of device for critical monitoring, but rather on the doctor.

Most of the time, smartwatches and fitness bands measure accurate heart rate pretty well, but using this device for monitoring critical heart rates is not a means. You can use these types of portable devices as functions, not medical devices.

I hope this information has helped you understand the functionality of the heart rate monitoring of smartwatch and fitness tracker.

About rahul

Rahul works as a Digital Marketing Executive. He develops innovative ideas and plans to market and promote various products and services of the company

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