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.
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.
