Smartwatch
How does Smartwatch measure heart rate?
Smartwatches generally use a technology called photoplethysmography (PPG) to measure heart rate.
It uses green LEDs on the underside that shine light into the skin, then uses a light sensor on the same side to detects the light that bounces back. Red blood cells absorb green light well. So, when heart beats and pumps blood through the wrist, more green light gets absorbed at each pulse. The amount of reflected light therefore changes, and the light sensor picks up these fluctuations. A software algorithm in the smartwatch then analyzes these changes in light intensity and calculates the heart rate based on the frequency of the peaks.
The green light is used because it’s readily absorbed by blood but not as much by the other tissues.
Some advanced smartwatches may have ECG (electrocardiogram) capabilities, which directly measure electrical signals from the heart for more precise readings.
How does Stress Monitor work in a Smartwatch?
A smart watch measure stress levels by analyzing the body’s physical reactions, typically through heart rate and heart rate variability (HRV) using its built-in sensor. The collected data is then used to estimate stress levels.
Additionally, some smart watches can combine heart rate data with measurements of skin’s electromagnetic conductivity to provide a more comprehensive approximation of stress levels.
Does the smartwatch sensor harmful to human skin?
The intensity of the green and red LED in smartwatches are typically very low and pose minimal risk. Thought, there are report about the light sensor on smartwatch burnt the skin on Fitbit Community forum, and from my own personal experience, which I believe it caused by putting on the watch while it’s still warm right off the charger.
If you start to experience any skin irritation or other discomfort on your wrist, such as redness, soreness, tingling, numbness, burning or stiffness, remove your smartwatch. If any of those symptoms persist, please contact a dermatologist.
Should I turn on Wi-Fi on smartwatch?
If your watch supports Wi-Fi, it can stay connected to your phone at any distance when they’re both connected to the Internet.1
Download speed will be much faster than Bluetooth.
References
“What still works when you leave your phone behind”. Wear OS by Google Help. Archive from original on January 14, 2024. Retrieved on January 14, 2024. ↩︎