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Comment by maven29 | Hacker News Reader

Just like the heart rate monitor, this was also moved into smartwatches for optimizing revenue from those who truly need it.

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Are you saying that smartphones used to have heart rate monitors but they were removed to force people to buy smart watches?

Any phone that can record 120fps video has a heart rate monitor, if you can calibrate it.

I forget which generation it was now, but many years ago I had a Samsung Galaxy phone that had a sensor that could measure your heart rate if you put your finger over it

The Galaxy S7 definitely had this feature.

The problem is, it was basically useless. The main use case for heart rate monitoring is continuously throughout the day/night, or during exercise. A watch is very good at this. An optical sensor on the back of your phone is not.

Periodically checking your heart rate by holding your phone in a specific way is not a useful feature for that many people.

For me, just having something that you can check 1 time per year is much better than nothing. The anecdote: I was working two heavy manual labor jobs 7 days per week and felt absolutely fantastic, glowing with power. Turned out the heart rate at rest was 180 lmao. Like a rabbit. Took a few days off, it dropped below 70.

If your heart rate at rest is truly 180, you have an arrhythmia and need to see a doctor.

It should decline some 60 sec after physical activity. I think I measured after 10-15 minutes. Fatigue, dehydration, lack of sleep, a diet with lots of coffee. I just added those to the todo list. I went home to sleep (and confiscated the heart rate meter), the next morning it was around 100 bpm which is still terrible shape. Over the day it sunk to 80, over the 2nd day to 70, 3rd a bit lower. Back at work it would barely elevate. The moral of the story: Don't work out 11 hours per day for 6 months straight.

+1. If a phone has a stopwatch, you can get your bpm at a given moment with a finger and a multiplication (or patience). Given the limited real estate on a mobile phone it's crazy to devote any space for something so trivial.

It's not a separate sensor- 30fps on an iPhone was more than enough.

Turns out, when you have a known luminance, white balance, and frame-rate... the DSP to grab heart rate from a finger is trivial.

Cameras can do it, yes.

But on the Galaxy S7 that I think is being alluded to here, it was definitely a separate sensor -- a MAX86902, IIRC.

The heart rate monitors in Google and Fitbit devices are insanely inaccurate during exercise. I had suspected as much already. Whenever a brisk walk indicated my pulse was 150 or so. But first, I could not reproduce this wearing a halter device and later I could not reproduce this wearing a polar heart rate monitor or a Frontier X2 ECG.

Conclusion, Fitbit and Google heart rate monitors on those wearables are hot garbage. Cue some snooty googler insisting I'm doing it wrong somehow.

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