Best Smartwatch Sensors And How They Work

Advanced health monitoring and fitness tracking features are being added to smartwatches and fitness trackers. But have you ever wondered how they manage to achieve it? We’ve gone through eight smartwatch sensors that can be found in the current devices, as well as how they work, in this article.


The pulse sensor is one of the most used smartwatch sensors. Have you ever wondered why a smartwatch or fitness tracker has a flashing green light? Smartwatches and fitness trackers measure blood circulation near your wrist and illuminate it with LEDs to determine your heart rate. Green was chosen because human red blood absorbs it strongly, allowing optical sensors to accurately assess blood flow and heartbeat.


Although GPS is an old technology, it has only recently been used in fitness trackers as CPUs have become more powerful.

A network of 29 satellites in orbit make up the global positioning system. To ascertain an exact location, an individual must be within four satellites’ range at any given time.

The satellites transmit a low-power, high-frequency radio signal to the GPS receiver. The time it takes for a signal to reach your smartwatch may be converted to your distance from the satellite using data from enough satellites, which can then be interpreted into accurate coordinates. Although GPS processors are improving their energy management capabilities, GPS is still a power-hungry sensor when compared to other sensors.

GPS, as opposed to basic step counting, enables runners, hikers, and cyclists to quickly chart their workout and assess the environment where they are.

Blood Pressure

Using Pulse Transit Time, a smartwatch can measure blood pressure using two sensors (PTT). The optical Heart Rate (PPG) sensor comes first, followed by the electrocardiogram (ECG) sensor. These two sensors on your smartwatch measure Pulse Transit Time (the time it takes for a pulse to travel from your heart to your wrist). The pulse travels quicker when blood pressure is high, and it travels slower when blood pressure is low.

The blood pressure computation begins when the user places their finger on the ECG sensor. A single-lead ECG signal is recorded, with each R-peak large spike indicating a cardiac contraction — about when a pulse leaves the heart.

The pulse then travels down the arm until it reaches the PPG sensor on the device’s underside, causing a pulse wave to appear in the PPG waveform. The pulse transit time is the time between the R-peak of the ECG and the pulse wave of the PPG waveform, which is how long it takes for a pulse to go from the heart to the rest of the body.


Pulse oximeters, often known as SpO2 sensors on fitness trackers, measure the amount of oxygen in the blood. Smartwatches are increasingly featuring finger-based pulse oximeters. Medical-grade and wearable oximeters both require light to function.

A pulse oximeter normally includes two LEDs, one red and one infrared, with different light wavelengths. The differential in light absorption between blood with high blood oxygen levels and blood with low levels of oxygen is the reason behind this. Blood that is oxygenated absorbs more infrared light than blood that is deoxygenated. Pulse oximeters may use this information to detect oxygen levels quickly and non-invasively, as well as monitor how well oxygen is transported to the extremities.


Smartwatches such as the Apple Watch 6 and 7, the Samsung Galaxy Watch 4, and a slew of other fitness trackers use heart rate sensors. They provide us constant updates on our heart rates, which we may use to determine how stressed we are.

Other heart rate exercise measurement technologies, which can open new health and wellness insights, have been released in recent years by watch manufacturers. The one most linked to an increase in stress monitoring is heart rate variability.

The temporal difference between heartbeats is used to calculate HRV (heart rate variability). HRV readings focus on the tiny changes of the heart, as opposed to monitoring beats per minute.

What, on the other hand, may cause such shifts? Factors include age, body posture, time of day, and current health status. Emotional, bodily, and behavioral experiences, on the other hand, are universal.

Having a high heart rate variability is typically believed to be a good thing. A low HRV level is frequently linked to stress. Diabetes, heart disease, and excessive cholesterol are some medical issues that are linked to those who have a low heart rate variability.

Fall detection 

Is a process that involves detecting the presence of a person who has fallen

Smartwatches can detect sudden changes in body motions and indicate whether a person has fallen. The technology will evaluate a person’s body posture, physical activity, and movement acceleration smoothness. If the system determines that these factors are in the danger zone and that a fall has occurred, an emergency fall warning will be triggered, and the user’s designated SOS contact will be contacted.

Urgent action 

When utilized properly, a smartwatch with fall detection will detect a fall and quickly alert emergency responders (if the device has wifi, LTE or is connected to a nearby smartphone). The emergency services will analyze the issue using the smartwatch’s mic and speaker if it can make calls.


The electrical function of the heart is tested by an ECG (electrocardiogram).

Each heartbeat sends an electrical pulse through the body. As a result, it contracts and pumps blood throughout the body. This electrical wave is measured using an ECG to determine the user’s muscle fitness.

Calculating the quantity of electrical activity in the heart and the interval between heartbeats is how this is done. This will help determine whether the heartbeat is regular, sluggish, fast, or unpredictable. It can also tell if some parts of the heart are overly large or overworked.

Is there a difference between an ECG and an EKG?

The way the acronym is spelled is the only distinction between ECG and EKG. ECG stands for electrocardiogram or electrocardiograph, which are both English terms, but EKG stands for elektrokardiogramm, which is the German spelling. The sensors are otherwise functionally identical.

Skin temperature 

monitoring on smartwatches like the Fitbit Sense is similar to SpO2 in that it does not do calculations on demand and instead displays deviations from the norm in a graph. A skin temperature sensor is used beneath the watch to do this. It’s safe to say that it won’t be taking the place of your thermometer any time soon. You must record sleep for a minimum of three nights in order for the Sense to build a baseline.

We hope this has given you a better understanding of the technological powerhouse that resides within that small computer on your wrist!

While the Fitbit Sense was the first fitness tracker to offer this advanced capability, numerous inexpensive fitness trackers do as well.


The more trackers you have, the greater picture you’ll get of your general health and well-being. Just remember to keep an eye on the battery life of these devices. The cost of a jam-packed piece of technology isn’t just the money; it’s also the time spent plugged into a charger.

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