Hmm … Where does Apple Watch know my pulse? Why they glow green

Is it possible to determine the pulse with the help of a pair of green “flashlights” on the back of Apple Watch? It turns out, yes.

In this article we will describe how Apple Watch determine the pulse, why this feature can be useful, how to improve the accuracy of measurements and monitor health through the clock.

It’s not clear to me: how does Apple Watch generally determine the pulse?

That’s it for this they are glowing green.

Built-in Apple Watch pulse meter works on the principle of photoplethysmography. What it is?

The photoplethysmograph fixes the blood flow with the help of two elements: a flickering LED and a photodiode that reads its reflection.

With each stroke of the heart, the volume of blood in the wrist increases, and between blows it decreases.


Blood absorbs green light and reflects red. A pair of Apple Watch LEDs blink at a rate of several hundred times per minute, and two photodiodes fix the amount of reflected light.

So they catch the pulse and can differentiate the heart rate range from 30 to 210 beats per minute .

If the watch hangs too freely, they automatically increase the brightness of the LEDs and the flicker frequency.

An interesting fact: when Apple Watch controls the pulse in the background, they switch the photodiodes to infrared mode. We do not see it.

I wonder how to know your pulse right now?


Nothing is easier:

1. Put on an Apple Watch if they are not on your wrist.

2. Open the “Pulse” program on Apple Watch.

3. Wait for the clock to complete the measurement.

With this application, you can measure the pulse, when you relax and walk *, do breathing exercises, exercise and recover from physical exertion.

If you need quick access to “Pulse” , add it to the list of favorites in the Dock Apple Watch (via iPhone) or display a shortcut on the dial.

And the health problems of Apple Watch is determined by the pulse?

Yes! This is an important feature of the watch.

Apple Watch controls the rapid pulse – tachycardia . This symptom is manifested during poisonings, fevers, endocrine diseases and problems in the work of the heart.

When you are at rest, and the heart beats faster than the given limit for 10 minutes, the clock reports this *.


Enable this feature:

1. Launch the Watch program on your iPhone.

2. Open the “Pulse”.

3. Go to the “High pulse”.

4. Determine the limiting pulse at rest in the range of 100 to 150 beats per minute.

To determine the normal heart rate in a calm state, start “Pulse” when absolutely relaxed. Or use the average value that the Pulse application defined.

But keep in mind that these data can be distorted if you recently took medication, ate black chocolate, drank coffee.

* – the first Apple Watch, which started selling in 2015, does not determine the pulse at rest and on a walk, do not support notification of increased heart rate.

Really, and in training from this there is real benefit?


If you regularly exercise, be sure to use the “Training” application on Apple Watch.

During exercise, the watch continuously determines the heart rate, and the heart rate monitor does not turn off for another 3 minutes after the end of activity.

Apple Watch combines information about the pulse and other data to estimate the number of calories that could be burned.

And what with accuracy: Apple Watch really not deceived?

Apple Watch is not a professional medical device. Therefore they can give only recommendations. If you are notified of an increased heartbeat, consult your doctor.

How to improve the accuracy of the Apple Watch?

1. Place the Apple Watch on the upper side of your wrist. The clock is not designed to read information from the bottom.

2. When doing sports or simply measuring the pulse, tighten the strap more tightly. But he should not squeeze his hand so as not to distort the testimony.

This is enough for the heart rate monitor to show the most accurate values.

That’s all. Now you will not be surprised when the clock on your hand suddenly flickers green. They just watch your pulse.

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