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Are Temperature Guns Accurate? Here's How The Coronavirus-era Thermometer Substitutes Work

Amid the Coronavirus outbreak, usage of infrared thermometers has increased. How do they function & how accurately can they measure human body temperature? Read

Temperature gun

The number of cases of novel Coronavirus are increasing around the world at an alarming rate and nations are taking steps to tackle the deadly virus. Ever since the outbreak of COVID-19, as a precautionary measure, there has been a need to routinely check body temperature. People are checked at airports, offices, stores and even in residential areas by guards/officials wearing masks with the help of infrared thermometer which is commonly known as 'temperature gun or 'infra gun'. 

This thermometer is used instead of a mercury thermometer as it gives out results faster and also because it can measure surface temperature without touching people’s skin. So how does this device function and how accurately can it measure human body temperature?

How do infrared thermometers work?

The device is equipped with an infrared sensor that can quickly measure surface temperature without making any contact with a person’s skin. Infrared thermometers work based on a phenomenon called black body radiation. According to the website '', the following is the method which shows how infrared thermometers work:

"Infrared light works like visible light--it can be focused, reflected or absorbed. Infrared thermometers usually use a lens to focus infrared light from one object onto a detector called a thermopile. The thermopile absorbs the infrared radiation and turns it into heat. The more infrared energy, the hotter the thermopile gets. This heat is turned into electricity. The electricity is sent to a detector, which uses it to determine the temperature of whatever the thermometer is pointed at. The more electricity, the hotter the object is."

How accurately do temperature guns predict results?

Experts say thermometer guns aren’t as accurate as mercury or digital thermometers, but they can be useful in some situations. The accuracy of the results also depends on how these devices are used, for example, how far it is kept from the body it is measuring, how steadily it is held and for how much time. The temperature can get affected by various factors such as wind and water.

Thermometer guns and thermal screening cameras, which measure the heat coming off a person, will not catch everyone infected with COVID-19, because there are some who are infected but show no symptoms, according to experts. 

Research published in The New England Journal of Medicine in February showed two of 126 people evacuated to Frankfurt in Germany on a flight from China’s Hubei province had tested positive for the coronavirus after arrival despite passing symptoms-based screening before boarding the plane.

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It can take from 2 to 10 days for a person to show the symptoms of coronavirus and the WHO has recommended a quarantine period of 14 days. If a person is affected by the virus and has not started to show symptoms yet, the infrared thermometer would not be able to detect. So, infrared thermometers might not provide an accurate estimation of the infected people.

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According to a prominent US publication, the thermometer guns used in screenings are "notorious, not active and reliable" since many screeners hold them at the wong distance or use them in the wrong environment. A report from CNA indicates that even if these devices are not that accurate in measuring body temperature, they can be used as a complementary tool for initial screening, followed by other necessary procedures.

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Despite the flaws, the non-contact thermometers or temperature guns have become scarce in the market and are being sold at a very high cost which is why people are finding it difficult to procure them.

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