Ear thermometer turns out that the eardrum is an extremely accurate point to measure body temperature from because it is recessed inside the head (just like your tongue). The problem with the eardrum is that it is so fragile. You don't want to be touching the eardrum with a thermometer.
This makes the detection of the eardrum's temperature a remote sensing problem. Granted, it is not very remote -- just a centimeter or so. But it's remote nonetheless! It turns out that the remote sensing of an object's temperature can be done using its infrared radiation. This technique is a very good way to detect the temperature of a person's eardrum.