There's some information about it here, it's more about children though:
https://synappsehealth.com/en/articles/i/mody-is-diabetes-in-children-always-type-1/
'In electronic touch [or digital] thermometers, the element responsible for temperature measurement is the electronic circuitry termed the thermistor (a type of resistor). Most of these devices are designed to measure the temperature in the mouth, axillary (armpit) or rectum (anus).' Source