Slide show: Choosing a thermometer

If you're over 30, you may not recognize all the temperature-taking gadgets shown here. On the far left is a plastic strip with liquid crystals that react to heat. Moving clockwise, the others are a digital pacifier thermometer, a tympanic (ear) thermometer, a regular digital thermometer and a glass oral thermometer that contains a mercury substitute.

You probably remember glass mercury thermometers from your childhood. When broken or thrown away, these thermometers release mercury, a toxin that pollutes the environment and, in large amounts, causes brain damage. If you still have an old mercury thermometer, ask your doctor how to dispose of it safely.

Digital thermometers are powered by button batteries and use electronic heat sensors to record body temperature. They can measure temperature orally, rectally or in the armpit (axilla), in 30 seconds or less. Some models come with disposable plastic sleeves to change with each use to ensure that they're sanitary. Most digital thermometers beep when the peak temperature is recorded. The result appears in a readout window on the flat upper side of the thermometer stem.

If your child already uses a pacifier for self-soothing, you may want to try a digital pacifier thermometer. It is sometimes difficult to get an accurate reading because your child must hold the pacifier portion in his or her mouth, without moving it around, for approximately three minutes. The peak temperature is displayed on the front of the thermometer. Digital pacifier thermometers tend to give slightly low readings, so doctors recommend adding 0.5 F to the recorded temperature.

A digital ear thermometer, also called a tympanic thermometer, uses an infrared ray to measure your child's temperature inside his or her ear canal. Ear thermometers are quick and accurate, measuring temperatures in less than two seconds. But they are not recommended for use in infants younger than 3 months, because babies' ear canals are usually too small.

These strips contain liquid crystal that registers temperature by changing color. Although they're easy to use, they're not precise. To get an exact reading of your child's temperature, use a digital thermometer instead.