Smartphones are notorious for not delivering- heck, my fitbit won't even give me an actual wrist temp value. Theres optical ones that can be built in a lab and

Smartphones are notorious for not delivering- heck, my fitbit won't even give me an actual wrist temp value. Theres optical ones that can be built in a lab and require profiling to an individual. The most accurate ones are still invasive- just not consumable fungus extract based. Maybe some biomedical company makes a reference design.