How does a smartwatch measure your heartbeat?

DW (English)

There are two ways wearables measure a person's heartbeat: optical pulse measurement using light and a heart rate sensor that records the heart's electrical activity.

Transcript

00:00 When it comes to accurate heart rate monitoring, we always recommend the classic chest straps.

00:07 It's an electrophysiological recording.

00:10 They essentially detect the heartbeats electrically, so they get a direct recording of the heartbeat.

00:16 But the problem with these, of course, is that you can't wear it all day or all week.

00:23 Smartwatches on the other hand are much more comfortable.

00:26 The heartbeat is detected via optical sensor, which emits a light signal to measure the

00:30 pulse wave.

00:31 But it's not quite as accurate.

00:39 The light is then absorbed by hemoglobin, a component of the blood from which we can

00:43 derive the heart rate.

00:46 But as it's a light source, everything that can interfere with light has an influence

00:49 on the data quality.

00:51 Things like skin color, body hair, tattoos or perhaps scar tissue.

01:02 Smartwatches don't work as well for people of color.

01:04 That's why a team at Google is experimenting with ultrasound, which would pick up the heartbeat

01:09 in the ear, via headphones, irrespective of skin color, light reflections or strong movement.

01:17 Besides heart rate, conventional variables often record heart acceleration.

01:22 Other values like calorie consumption or blood oxygen levels are calculated using algorithms.

01:27 Exactly how they work, though, is a trade secret.

01:33 But in the end, the user only gets the results.

01:37 So you can't tell if it's actually high-quality measurements or how much has been calculated.

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