How Do Smartwatches Measure Heart Rate?

Today, technology has almost touched every field. Now, it’s time to have some advancement in the watches. From traditional watches that are analog or digital, they are now upgraded to smartwatches. These are such types of watches that help you with not only time but as the name indicates they are even smarter than the old traditional wrist watches. They provide you with different features that are monitoring heart rate, blood oxygen, tracking, footsteps, and navigation through GPS, and many more. They are now friendlier as compared to the old watches. These watches can do multiple jobs like sleep tracking, measuring heart rate, calories burnt, etc.

Besides sleep tracking, which I have discussed in how do smartwatches track sleep, here we will talk about how these watches measure your heart rate. What type of technology and procedure are they using? The heart is the main part of the human body if it works well, your body will be in normal condition but if there is any disorder regarding the heartbeat then the whole body gets disturbed. As for adults are concerned, they know what is happening to their heartbeat but the problem arises if there is any problem regarding your kid’s heartbeat, they neither know of it nor can they tell you that something is happening to their heart or blood pressure. So, to examine closely, you can have a smartwatch for them as some best smartwatches for kids are there in the market.

Photoplethysmography (PPG)

To measure heart rate, these watches use the technology of photoplethysmography or PPG. If you look at any smartwatch downside there you will see the green lights. It examines the heartbeat when your blood absorbs the green light. Blood is red in color because it reflects red light while absorbing the green one. When your heart beats, more blood flow through your arm and wrist and absorbs more green lights. In between the beat, it absorbs lesser. During a workout, these watches calculate your heart rate thoroughly while, in the rest position, it uses infrared light to measure the rate after every 10 minutes. Users also complain against the accuracy. This can be because of two reasons; sensors would be worn out, or wearing the watch loosely can also give an inaccurate reading.

To measure heart rate through some of the best smartwatches using the technology of photoplethysmography or (PPG) the user must have the following components:

Optical Emitter

The two lights that are on the back of the smartwatch are actually optical emitters. Some smartwatches utilize the light of multiple wavelengths. This is due to the thickness, morphology, or skin tone. The difference in wavelength is for different types of skin and tissues of the wearer.

Digital Signal Processor (DSP)

This component helps in reading the refracted light from the skin of the wearer. This reading then changes in binary numbers. Such reading is then transferred into heart rate data. Then it shows you the possible heart rate.


The accelerometer measures the movement of the hand. Such measures are then integrated with DSP and they work as input data for the PPG algorithms.


Primarily, they work on the input that is given by the accelerometer and the DSP to get the motion-tolerant heart rate data. Also depends upon the capability of the device. In addition, it is also used to find out the calories burnt, R-R interval, blood oxygen levels, VO2, and blood pressure.

Reasons for Inaccurate Reading

There are also some of the important reasons which disturb the accurate reading of the heart rate. Minimizing such reasons will help you in better and accurate reading. Following are those:

Light distributed

This is the big technical hurdle. This arises when the light emitted by the watch, most of the light absorbed in the body muscles, bones, etc. A very less amount of light returns to the sensors. Again in this less amount, a very tiny part of the light indicates the blood flow caused by the heart which disturbs the reading.

Skin Issues

Different people have different skin colors. Darker skin absorbs more green lights. Also, tattoos right on the place where PPG tries to calculate the data also decrease down the accuracy. These two reasons are also the hurdles for inaccuracy.

Multiple Tasks

Inaccuracy in reading also happens when a person does multiple tasks at the same rate as your pulse rate. The algorithms of the smartwatch become disturbs while reading the heart rate. This also adds inaccuracy.

Wrong Sensor Location

The wrist is actually not the best location to measure the heart rate because of the optical noise as we have mentioned above. The best place is the forearm where the blood vessels are prominent and denser that gives a better reading.


To sum up, the above discussion cleared the process of how smartwatches measure heart rate and the technology they are using. Also, I have given the reason why sometimes it did not give the correct readings. Besides all, these are the best devices that can help you check your heart rate anytime you want without going anywhere or calling a doctor. So this is the advanced technology and makes use of it rather than using it in waste materials.

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