[ksaj]

I would strongly expect sunshine to be enough to make it think you have a serious fever, or a snowball fight registering as a sudden and unexpected death.

For accurate readings, one usually goes internal (sublingual, otic, anal) or quasi-internal (closed armpit). Forehead readings are limited but able to detect fevers in controlled environments. The surface of your extremities are prone to big temperature swings that are completely unrelated to health, such as when you have cold feet or hands. I'm sure you can have a serious fever without the temperature being notable at the wrist.

[AaronFriel]

I'm sure that's true for a "one shot" reading, but having the sensor continuously attached and, indeed, two sensors (one outward facing, one inward), it seems plausible that they could have devised a new, accurate and continuous temperature measurement method.