How Do Fitness Trackers Work

Fitness trackers have become increasingly popular among people looking to lead an active lifestyle, love sports and care about their overall health. These are universal and multifunctional devices intended for:

  • Measuring pressure and pulse fluctuations;
  • Keeping track of steps and distance covered;
  • Controlling and maintaining the quality of sleep;
  • Controlling calorie consumption;
  • Monitoring physical activity;
  • Receiving notifications from a smartphone;
  • Getting sports alerts and recommendations.

To ensure that all analytical information is correct and for accurate results, basic information about the owner is entered into the application on a smartphone or tablet. This includes indicators such as age, weight and height, gender.

To determine if this fitness device is right for you, it is important to understand what these trackers do and how they work. This will help you decide exactly what features you need and the ones you can skip when on the shopping trail. 

Accelerometer and gyroscope (how does a pedometer work in a fitness tracker)

How Do Fitness Trackers Work


An accelerometer (G-sensor) is a device that determines the acceleration of an object in space. Thanks to the accelerometer data, a fitness tracker can count the number of steps you have taken, as well as the speed of movement. Fitness trackers are equipped with three-component accelerometers that track acceleration along three axes of coordinates.

Thus, the accelerometer built into the fitness tracker determines whether the wearer’s hand is at rest or is moving with a certain level of acceleration. Data of the acceleration of the movement of your hand is measured by the accelerometer and is transmitted to the microprocessor embedded in the fitness tracker, where it is then processed. 

A special algorithm is responsible for the processing, which determines whether the movement of your hand is connected with the movement in space or is it simply gesticulation. Top of the line and advanced gadgets can distinguish the type of activity (walking, running) as well.

The accelerometer can be used to not only determine the number of kilometers traveled but also to analyze sleep. Accordingly, the G-sensor will capture the slightest movement of a person during a night’s sleep. More advanced models can also use this algorithm to determine the phases of sleep.


A gyroscope is a device that tracks changes in the position of an object. In other words, the gyroscope calculates the angle by which the orientation of the object in space changes. In the case of fitness trackers, they are worn on the wrist hence serve as a subject.

Thanks to the gyroscope, the smartwatch microprocessor can recognize not only walking or running but also other physical activities. These include: 

  • Push-ups;
  • Swimming (for waterproof models);
  • Jumping;
  • Hiking.

The combination of an accelerometer and a gyroscope offers a comprehensive three-dimensional perspective of how your hand moves and allows you to improve the accuracy of counting your steps and auto-detecting the type of activity.

You may notice that some trackers turn on the screen when you turn your hand towards your face. A gyroscope is also responsible for this function. This is quite a useful feature that makes it easier to interact with the device.

But you’re probably asking yourself why the fitness tracker incorrectly counts the steps?

The fact is that a fitness tracker that is worn on the wrist is designed to analyze all your movements with your hands during the day. Some of them may be mistakenly calculated by the tracker’s algorithm due to poor quality. Such types of activity as driving a car, changing clothes, taking a shower and active gestures can cause false alarms with your pedometer. Also, the step counting algorithms do not take into account the many individual parameters that are common to each one of us.

It is precisely because of such false positives that the error in calculating steps by the end of the day can be up to 30%. It is worth noting here that the error of all fitness trackers varies since the accuracy of the readings depends not only on the installed accelerometer but also on the step counting algorithm.

There is nothing wrong with slight errors in the pedometers performance since the very essence of the fitness tracker is taking into account your activity, and not providing exact numbers. It is an indicator of the number of steps that should let you know whether you have spent your day quite actively. If you are an active girl who watches her figure and wants optimal accuracy in the testimony, I highly recommend getting acquainted with our article on the best fitness tracker for women, which will help you to play sports as effectively as possible and for the best results. 

Pulsometer – How it works and what is the accuracy

The technology that makes the heart rate monitor work is called photoplethysmography. It involves the use of green LEDs emitting light and detectors that record the level of its reflection. With the contraction of the heart, blood pressure increases and capillary blood flow increases. 

As a result, more light is absorbed and a pulse is determined and indicated with an LED light. This is a handy feature for people who monitor their heart rate during sports training, daily activities and even sleep. For the indicators to be as accurate as possible, the tracker must fit snugly against the skin’s surface.

In any case, the fitness tracker is not an accurate medical device, so the pulse rate rendered may not be 100 percent accurate. Characteristics for this method of measuring heart rate is the increase in error with an increase in the frequency of heartbeats, ranging from 100 beats per minute. But on a brighter note, the error of the heart rate monitor, in general, does not exceed 2%.

Measuring pressure in a fitness tracker

Fitness trackers with pressure measurement functionality are equipped with special sensors consisting of piezoelectric elements. The essence of these sensors is that under the pressure exerted on them, they produce electricity. 

Thus, the pulse wave from the human wrist is converted into electronic signals of the appropriate size, which are then sent to a special software interface. In this software, signals are processed and presented in the form of numbers that are familiar to us. The results will be rendered on the device display or in the application itself or you can even see them on your PC or MAC.

Of course, the most accurate readings can only be seen using medical devices. Information obtained through the smart tracker will be reliable only in 80% of cases. The average error for inexpensive models is from ten to twenty millimeters of mercury. This is not a significant indicator, but it should also be taken into account as it gives you a rough idea of where you stand in terms of stats.

The problem is that if the skin is covered with dust or sweat – the results will be less the most accurate results. This is the same situation if the owner of the device is actively moving (for example when running).

Monitor sleep phases

Human sleep consists of two main phases: fast sleep (REM) and slow sleep (deep). The last phase includes 4 more stages of falling asleep (the first two are superficial sleep, the second two are deep).

The phase of slow sleep is 75-80% of your night’s rest, while REM sleep takes 20-25%. Initially, rapid sleep occurs after 70-90 minutes of slow and lasts 5-10 minutes, but with each subsequent similar cycle of REM, the phase gradually increases and in the morning can reach 20-60 minutes. When morning comes around, the REM phase becomes more superficial and more and more like wakefulness.

Two sensors are used to monitor sleep phases in fitness trackers: an accelerometer and a heart rate monitor. The fact is that in the phase of deep sleep a person becomes immovable and the brain goes into rest and recovery mode. 

In such a state, the pulse of a person is slowed down (during sleep, the pulse can slow down by 1.5 times) and is monotonous. In the phase of REM sleep, a person has rapid movements of the eyeballs and brain activity is almost the same as normal, breathing and heart rate increase, pressure increases. 

But thanks to a heart rate monitor, which monitors the heart rate, and the accelerometer that keeps tabs on the slightest movements of the owner, it is possible to monitor the change of sleep phases, as well as waking up during the night. 

How a smart alarm clock works

To wake up pleasantly, most of the models have a feature such as “smart alarm clock”. It allows you to identify the most suitable moment for waking up thanks to the ability to control the change in sleep phases. The most favorable for awakening is the phase of REM sleep when the state of the human body is similar to the state during wakefulness. When you wake up during the REM phase, you will not experience fatigue and a desire to return to bed.

If you need to wake up at a certain time, you can configure the time in the tracker. The device will now automatically choose the most suitable moment for waking up. For example, if you need to come to work by nine in the morning, you can choose the period from 7:00 to 7:30. Then the tracker will wait for the onset of the fast phase of sleep in the specified time and as soon as this happens, the alarm will trigger on. If the REM sleep phase does arrive, the alarm will work at the very last moment i.e. at 7:30.

How does a fitness tracker count calories?

Almost all modern fitness trackers are equipped with the function of monitoring the number of calories burned, but do they all work the same way?

The fact is that a special mathematical model is responsible for measuring calories burned, which may offer varying results depending on the parameters it takes into account. The most complex models take into account the indicators of activity, physical condition, as well as anthropometric indicators of the carrier. Simpler models do not use data of the physical state of the owner, and the simplest algorithms work only based on activity data.

Indicators of physical activity are calculated based on accelerometer data (see above). Main displacement measure – the number of steps completed and the data that are transferred to the mathematical model. Some fitness trackers also take into account the type of physical activity (running, walking, cycling, swimming, etc.) – such devices work more precisely because the consumption of calories with different activities is not the same.

Physical indicators allow you to more accurately determine the energy costs and the user of a fitness tracker. These indicators include pulse rate, blood pressure, and blood oxygen saturation level. The more metrics the tracker takes into account, the more accurate the calories results will be. 

Anthropometric indicators are set by the user in the fitness tracker application. These are height, weight, age, and gender. Information about the owner is very important in calculating the calories burned, so the trackers that do not take into account these indicators will be inaccurate.

Thus, for accurate calorie counting, it is best to choose a fitness tracker that uses the maximum number of parameters in its algorithms. But even in this case, the error is probable, since fitness trackers are not accurate devices, they only approximately show the overall picture of your body’s physical activity.


It is worth noting that sensors embedded in “smart trackers” differ in their sensitivity and quality. In more expensive models, they are much more sensitive, which means that the results will be the most reliable. Also, the problem of functionality can be on the software side, so when choosing a fitness tracker it is recommended that you consider the following factors:

  • Functionality;
  • Appearance;
  • Information about the manufacturer;
  • Reviews of verified users;
  • The accuracy of the functions;
  • Cost;
  • The presence of marriage.

If you have a child and you want to add more new colors to his life and introduce them to the world of gadgets, then check out manufacturers who make the kids fitness trackers geared towards kids.

If you have any questions, feel free to ask them in the comments.

DemystifyingDigital Team

High-quality content can only be written by experts in the field. The DemystifyingDigital team consists of just such people. Our specializations range from cameras to smartwatches. We are constantly following the latest developments in technology. Each of us has a desire to grow our knowledge in order to provide only the best information to our readers. The world of gadgets is wide, and to cover the many types of technology we are constantly recruiting professionals to join our team. Thus, we increase our expertise and make our work even better.

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