How is that predicting in advance though? Sounds like it measured active symptoms like a change in body temp etc. That's not prediction, that's reaction.

I think it is fair to assume they meant before symptoms? Which, yes, your heart rate is a symptom. No, it isn't one most people consider.

Device detects 0.1 degree average temp increase. I don’t.

Like your car will start with a small noise first, you can’t hear it. But in time the small noise becomes a big noise just before things break.

If you catch it in the small noise part, you can proactively prepare.