Core temperature reading is the only reading that matters. Wrist temperature varies a lot for reasons that have little to do with a core temperature variation. Core temperature can easily and reliably be measured at forehead or hear, if they cared about this all they needed was a la IR sensor that the person can, if they feel like they might have high temperature, put near the forehead.Enjoy walking around with your rectal thermometer dongle for your Apple Watch then lol, the reading it provides is more than sufficient for most uses. A core temperature reading is not necessary in a lot of instances.