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Comment by _qua | Hacker News Reader

I used to be someone who might have a single beer with dinner a few nights per week. When I got a Garmin and saw what it did to my stress levels and sleep, I essentially stopped drinking at all except for rare social situations.

In addition to improving the numbers, I noticed a qualitative improvement in my sleep, energy levels, and exercise recovery.

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I had the same experience. It puts things into circumspect when you can physically see how erratic things like heart rate and sleep stage times differ with just a single drink. The difference for my was so stark you'd think it were a bug if it weren't for the fact I could spot the pattern and test to see the truth of things.

OK but once you've learned this fact (that I think you could have learned from numerous sources without any technology), what is the ongoing value of the sleep tracker? I feel it is in the category of things that you learn from but then stop needing, including a cadence meter on a bicycle, bathroom scales, and similar devices.

You never really know when it might matter. One huge thing is when I have a serious illness I can see my heart rate remains about 80bpm all night long. I know my immune system has quieted down when my nighttime heart rate gets back down in the 50s. This doesn't even require accurate sleep tracking. (In fact the watch has a hard time even noticing I'm asleep when I'm that sick, but it doesn't really matter, it's very useful.)

I also notice similar things related to heavy exercise etc.

Do you not get fever dreams? Even if I have a slight fever (say 100) my dreams are uniquely different, so I always know when I have a fever at night. Hard to explain "fever dreams" if you don't get them...

I've seen my heart rate elevated when I don't have a fever, and it can take several days to fully recover. Also no, I don't get fever dreams.

It's like the speedometer on your car. Even once you reach the speed limit, you may need to check your speedometer again and again, both for safety and comfort. Consider that different people place a different value on their health. In a high stakes environment like a school zone, you would prefer to check your speedometer more often. Also consider that the accompanying apps are gamified, as in addiction forming.

You can dial in several things if you know how well you slept:

I can judge how performant I'll be in the gym and fitness competitions - ie, how well I can push myself and recover. I can work out whether what I ate before I slept had an impact (high cards vs low, or if certain foods are a trigger for poor sleep). I can understand if things like meditation, light sources, and noises outside, among others, actually impact me or not. I'm constantly learning something new from it month by month.

What are measurements for stress levels? Are they accurate enough?

I may be wrong, but I think it's just heart rate and heart rate variability.

I find that I can pretty consistently see an increase in resting heart rate by several beats per minute the day after drinking, an elevated skin temperature and a reduction in Deep- and REM-sleep. Particularly heavy drinking will manifest itself as a large drop in heart rate variability.

Garmin wearable devices display a proprietary stress metric from their Firstbeat Analytics subsidiary. This is basically just heart rate variability (HRV) normalized to the user's baseline.

https://www.firstbeatanalytics.com/en/features/all-day-stres...

As for accuracy, compared to what? Any definition of "stress" is inherently somewhat arbitrary and subjective. There seems to be a decent correlation to how I'm feeling. But the metric isn't really actionable for most people.

Whether the measurements are accurate enough is not clear, but they are certainly precise enough. I (and all my friends) can easily see huge differences in HRV on nights of drinking, it's pretty amazing.

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