Body temperature measurement, tracking or both are among the most hotly-discussed potential features for next-gen smartwatches. However, according to a respected security analyst, OEMs are having perhaps more trouble perfecting it than they may have imagined, even major players such as Apple. Currently, it is thought that more work is required to incorporate it into its series-8 Watch.
https://www.notebookcheck.net/Apple-Watch-series-8-units-with-a-body-temperature-sensor-upgrade-are-just-an-algorithm-away.616813.0.html