There are many different thermometers for many applications—the common mercury thermometer is used for measuring to within a degree, the thermocouple is used to electrically measure temperatures within a very wide range, and the pyrometer is used to observe and regulate temperatures above 1,300° C (2,400°F). One of the most sensitive devices for measuring temperature is the thermistor.

A type of semiconductor, the thermistor is usually constructed of metal oxides, such as nickel oxide or copper oxide, and then coated in epoxy to protect it. It works on the principle that electrical resistance within an electric circuit will increase as the temperature increases. Because the resistance within a circuit can be measured very precisely, the thermistor is able to detect temperature variations as small as 0.001° C. This makes it among the most accurate thermometers available. Thermistors are generally found in hospitals, coupled with a digital readout. They are also used in other biological environments, particularly those that require careful measurement.