Three primary types of thermometers are on the market for consumers.
Digital thermometers record body temperature through electric heat sensors. They can be used in the rectum, mouth or under the armpit. However, armpit temperatures are typically least accurate.
Digital ear thermometers use infrared scanners to measure the ear canal temperature. Earwax or an abnormal ear canal can interfere with the accuracy.
Temporal artery thermometers also use infrared scanners, measuring the forehead’s temporal artery temperature. These thermometers can be used even while a child is sleeping.
Digital pacifier thermometers, fever strips and mercury thermometers are not recommended, advises Mayo Clinic.