Mercury glass thermometers, although hard to read, have been used for years to measure temperatures in the rectum, mouth or under the arm (but not the ear). They are no longer recommended because they can break easily and release toxic mercury.
Electronic digital thermometers offer a number of advantages over glass thermometers. They obtain temperature readings faster, and their digital display is easy to read. There is also no risk of injury from broken glass or mercury.
Infrared thermometers measure heat generated by surfaces and cavities. The key advantage of this type of thermometer is its speed – it takes only seconds to obtain a temperature reading.
Infrared ear thermometers measure the heat generated by the eardrum and surrounding tissue. They give an accurate temperature on an easy-to-read digital display in just a few seconds.
Infrared forehead thermometers use the forehead to take a temperature in a gentle way. Forehead thermometers measure the infrared energy emitted from the skin above the eyebrow area and the surrounding tissue. This energy is collected through the lens and converted to a temperature value. The accuracy of the thermometer depends on the type of technology used. Forehead thermometers can measure temperature by touching the forehead or from a distance.