June 7, 2022, 4:00 pm | Read time: 2 minutes
Smart watches, known as smartwatches, have evolved into true all-rounders in recent years. But how exactly do these wearables measure body data?
Smartwatches like the Apple Watch not only display the time and measure the pulse. Modern smart watches can also determine blood oxygen levels, track and analyze sleep, have GPS on board, can be paired with 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
By now, almost all smartwatches have both position and acceleration sensors. These sensors can fairly accurately detect how you move 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 roughly determine how lightly or deeply you sleep based on movements and pulse.
Many smart watches also have a so-called heart rate monitor integrated. This is an optical sensor on the underside of the watch case. Green LEDs illuminate the veins and blood vessels on the wrist. When the heart beats, more blood flows, absorbing the green light. Between beats, less blood flows, and more light is reflected back to the sensor. By continuously measuring the heart rate, a smartwatch can also detect irregularities that may indicate heart problems and provide warnings.
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ECG and Oxygen Saturation
The measurement of blood oxygen saturation (SpO2) works in a similar way. Oxygen-rich blood is bright red, while oxygen-poor blood is darker red. Instead of green light, infrared light is used in this case.
A few smartwatches, including the Apple Watch, also have an ECG sensor. The necessary electrical heart sensor is built into the rotating crown and the glass back of the smartwatch. The watch can thus detect sinus rhythm or atrial fibrillation. The waveforms are stored and can be shared with a doctor if needed.
Typically, every smartwatch comes with a smartphone app that supports its functions. All the data from the smart watch is sent there and processed accordingly. However, the wearable can perform an initial evaluation based on the measured values itself. Combined with other features like GPS, very detailed analyses and evaluations are now possible.