There are several kinds of medical thermometers for measuring the temperature of humans or animals from various locations on the body, mainly under the tongue or armpit, in the rectum or ear, as well as in front of the forehead. Mercury-filled and digital thermometers are the most commonly seen in our daily life. They are widely used at home and in clinics or hospitals. Plenty of shops or restaurants also require customers to measure the temperature before entering during COVID-19 pandemic.