Thermometers are important for Covid and fever testing

Medical thermometers measure temperature of anything, but most of use a thermometer in the home as a medical device to detect a fever. A fever is a rise in body temperature which is usually caused by an infection. This is actually a sign that the body is fighting off an infection. 










38 or above 

Seek advice 



Take medical advice for relief of a temperature. You should keep hydrated as you will lose fluids through sweating. Cold baths, ice cube baths, or alcohol baths or rubs can be dangerous and should be avoided 

Health Line


Thermometer options

Check out our Thermometer store

Infrared Non-Contact  

 The latest in point and shoot thermometers. Non contact stops transmission and is therefore safer. 

Digital Thermometers 

These are used by contacting an area of the body to the tip of the thermometer. Either : 

  • Oral (under the tongue) 4+ years of age 
  • Rectal – babies but be careful. 
  • Armpit – this is the least accurate but the safest 

Tympanic or ear 

These measure infrared heat in the ear.  

Note that these are not recommended for babies or for people with wax build up or when they have an earache 

ear thermometer

Understanding Scales – thermometers

The concept of the original thermometers was to measure the movement of a liquid. There are three visible states of a liquid, frozen, liquid and boiling. By using the extremes as a start and stop you can make a scale up. However, it is normal for us to use traditionally calculated scales for consistency. These are Clecius, Fahrenheit and Kelvins.  

Fahrenheit water freezes at 32 degrees Fahrenheit and boils at 212 degrees Fahrenheit, This scale is used in three countries, the USA, Burma and Liberia. 

Celsius scale – is a part of the metric system, whereby freezing point equals zero, and boiling point 100 

Kelvin scale is used by physicists and scientists who require precise temperatures. It is the only unit of measure that that includes absolute zero, where there is a total absence of heat. Water freezes at 373 kelvins and boils at 373 kelvins.




Liquid Thermometers. The concept being that liquid expands when heated. The preferred choice of liquid is in fact a metal call mercury.  


Liquid thermometers cannot be used to measure temperatures in Kelvins. They work on the principle of detecting tiny variations in radiation. They use an instrument called a thermistor which can change its resistance to an electric current based on temperature.  

Infrared thermometers are used by Astronomers as they can measure temperatures in space.  

Pill thermometers are used by athletes to prevent heat related illness. They are swallowed, the pill transmits information about the body core temperature for between 18 and 30 hours.  


Nanothermometers were developed at Harvard University and are able to measure temperature variations in a single living cell. 

 National Geographic


History of the thermometers 

Many authors believe the Greek mathematician and engineer Hero of Alexandria should be credited with the invention of the thermometer. (10-70 AD).  

Several European scientists in the 16th and 17th centuries, (Galileo Galilei and Santorio Santorio) developed the idea. As a result, devices were shown to produce this effect reliably, and the term thermoscope was adopted because it reflected the changes in sensible heat. The difference between a thermoscope and a thermometer is that the latter has a scale. Though Galileo is often said to be the inventor of the thermometer, there is no surviving document that he actually produced any such instrument. 

The word thermometer (in its French form) first appeared in 1624 in La Récréation Mathématique by J. Leurechon, who describes one with a scale of 8 degrees. The word comes from the Greek words θερμός, thermos, meaning “hot” and μέτρον, metron, meaning “measure”. 

Remember – when in doubt always contact your health advisor