There are currently a number of smartwatches on the market that offer health tracking. We focused on individual health features, their reliability and usefulness, and compared products that offer these health features.

Smartwatches are capable of measuring blood flow in the skin beneath the watch using an optical sensor. Light is shone through the skin, and the light reflected from the wrist back to the watch is detected. The individual peaks in the light curve correspond to pulses of blood flow, allowing the heart rate and its regularityto be determined. This allows for the detection of heart rhythm disorders, particularly atrial fibrillation or extrasystoles. By using two specific wavelengths of light, arterial blood oxygen saturation can be determined. The blood flow curve also changes in slower waves in sync with breathing, allowing for the determination of respiratory rate or respiratory arrest. By analyzing the shape of individual pulses, blood pressure can be estimated if the watch is calibrated by entering a conventionally measured blood pressure at the time the curve is recorded. However, this method is inaccurate and is not currently recommended. Some manufacturers simply alert the user if the heart rate curve suggests high blood pressure and recommend measuring blood pressure using the traditional method. By using a specific sensor wavelength, carotenoid levels can be determined, which may reflect the body’s stress levels.

An ECG , or electrocardiogram, is another possible function of a smartwatch. It is a record of the electrical signal emitted by the heart during its activity and can be read from the surface of the body after two electrodes are placed at a sufficient distance. In practice, it is necessary to place a finger of the other hand than the one on which the watch is worn on one part of the watch and the watch then reads the signal between both upper limbs and records a single-lead ECG. The quality of this ECG is usually very good and can be used to diagnose a number of heart rhythm disorders or to confirm a natural heart rhythm.

The built-in accelerometer can measure even subtle movements and changes in position, allowing you to estimate the type of movement (walking, running), detect falls , detect sleep quality and respiratory arrests during sleep , and data from the sensor can also be used in combination with the shape of the plethysmographic curve to estimate the risk of hypertension.

Smartwatches can also monitor skin temperature and use it to track menstrual cycles and estimate ovulation dates .

Another possible function of a smartwatch is to measure blood pressure using the classic method using a pressure cuff built into the watch strap. This method is accurate and can therefore be used to measure pressure, unlike the above method of analyzing the photoplethysmographic curve. Only two products on the market currently have this function.

For some functions, manufacturers have already obtained medical device certification - this must usually be preceded by a clinical study that confirms the effectiveness and safety of the given method. Most manufacturers have certified ECG recording and heart rate monitoring, some have certified sleep apnea detection or blood pressure measurement or hypertension estimation. An overview of individual health functions of the main smartwatch models, including certifications, is given in the following table.

*Overview of health features of the main smartwatch models on the market*

A more detailed description of the health functions and limitations of individual smartwatch models is provided below. These are the most common models on the Czech market, mostly the “flagship” models of the given manufacturer. In many cases, cheaper models can also be found from the given manufacturer, which have limited functions, differ in battery life, design, etc.