[gruez]

>I've also heard of an acquaintance that they cancelled plans because their (Garmin™) Body Battery was too low.

I wouldn't take that at face value. Sounds far more likely that they already wanted to flake and needed an excuse.

[fwipsy]

Yep. I expect they were feeling tired and the smartwatch readings just confirmed it. If they really felt like coming, the readings wouldn't stop them.