Everyday Tech Part 6: How a smartwatch feels your pulse
Green LEDs shine into your wrist; blood absorbs green light, so with every heartbeat a light sensor sees a tiny dip and counts the beats.
How does your watch know your heartbeat? ⌚❤️
💚 Flip it over: green LEDs flash on your skin — hundreds of times a second.
🩸 Blood is red because it soaks up green light. A light sensor reads what bounces back.
💓 Each heartbeat pushes more blood into your wrist → less green light comes back.
📉 So the light dips once per beat. 7 dips in 6 seconds × 10 = 70 beats a minute!
✅ Best reading: hold still and wear it snug (a loose watch lets outside light in).
Read the voiceover (transcript)
- How does your watch know your heartbeat?
- Flip it over: green lights flash on your skin!
- Blood soaks up green light. A sensor reads the rest.
- Each heartbeat pushes more blood in, so less light comes back!
- Guess: how fast is this heart?
- Seven dips in six seconds: seventy a minute!
- Hold still, wear it snug!
- Next: how tap to pay works. Follow for Part 7!
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