Smart watches, so-called smartwatches, have developed into real all-rounders in recent years. But how exactly do wearables actually measure body data?
Smartwatches such as the Apple Watch not only show the time and measure the heart rate. Modern smart watches can also determine blood oxygen levels, track and evaluate sleep, have GPS on board, can be connected to smartphones and much more. But how exactly does such a smartwatch work and how does it measure all these values from its position on the wrist? TECHBOOK explains.
Smartwatch function of optical heart rate measurement
Almost all smartwatches now have both position and acceleration sensors. These sensors can record relatively accurately how you are moving and at what speed. Based on the walking pattern, they can distinguish whether you are walking, running, sprinting or climbing stairs. At night, the sensors track sleep and can even use the movements and heart rate to roughly recognize how light or deep you sleep.
A so-called heart rate monitor is also integrated into many smart watches. This is an optical sensor on the underside of the watch case. Green LEDs shine through the veins and blood vessels on the wrist. As the heart beats appropriately, more blood flows, which absorbs the green light. Less blood flows between the beats and more light is reflected back onto the sensor. By continuously measuring the heart rate, a smartwatch can also detect irregularities that indicate heart problems and warn of them.
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ECG and oxygen saturation
Measuring the oxygen saturation in the blood (SpO2) works in a very similar way. Oxygen-rich blood is light red, while oxygen-poor blood is darker red. In this case, infrared light is used instead of green light.
A few smartwatches, including the Apple Watch, also have an ECG sensor. The necessary electrical heart sensor is installed in the rotatable crown and the glass back of the smartwatch. The watch can thus detect sinus rhythm or atrial fibrillation. The waveforms are saved and can be shared with the doctor if necessary.
For every smartwatch there is usually a smartphone app that supports the functions. All the data from the smart watch arrives there and is processed accordingly. However, the wearable can carry out an initial evaluation based on the measured values. Coupled with other functions such as GPS, very detailed analyzes and evaluations are now possible.