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.

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