How does the heart rate monitoring system work in watches?

29 Haz 18:33

Dude, the heart rate tracking system in smartwatches is actually based on a pretty simple physics principle: photoplethysmography (PPG). What’s that? Basically, it’s a method that measures changes in blood flow in the capillaries under the skin using light. LEDs on the back of the watch shine green light (mostly around 525nm wavelength) onto your skin, and a sensor picks up the reflection. If there’s oxygenated hemoglobin in the blood, some of the light gets absorbed, and the rest bounces back. Since blood volume changes with each heartbeat, the reflected light fluctuates—and that’s how they calculate your pulse. Now, about battery life—man, that’s where the accounting comes in. If the PPG sensor ran nonstop, the battery would die fast, but smartwatches fire it up in short bursts, like a camera flash. For example, they might emit light for 20-50ms every 2-3 seconds, then shut it down the rest of the time. That way, with standard use (8-10 hours of activity tracking a day), you get 2-3 days of battery life. With optimized chips like Qualcomm’s Snapdragon W5+, some watches can stretch that to 4-5 days. And yeah, there are modes that only activate during workouts instead of running all the time—smart move. Then there’s the signal processing in the background, which isn’t as simple as it sounds. You’ve got machine learning algorithms filtering out noise from the motion sensors (accelerometers), and medical-grade systems like Apple’s ECG mode take it even further by analyzing electrical signals directly—but that really drains power. So, watches are always trying to balance accuracy with battery life. It also depends on the sensor—fitness-focused models like Whoop 4.0 can last 5+ days, while Garmin Venu 3 can hit 10+ days.