Infrared Thermometers: Why They Are Unreliable in COVID Fight

Infrared Thermometers: Why They Are Unreliable in COVID Fight

3 min read
Hindi Female

Every housing society, every office building, grocery store and even your local salon has armed itself with an infrared thermometer gun. As lockdowns ease, these strange devices that have become a symbol of the fight against coronavirus, are popping up everywhere.

And while pictures of these guns have splashed across the world, the device first grew popular in early 2000s, first to check the growth of SARS and later, Ebola outbreak in West Africa.

So what are these guns and what do they do? Also, are they accurate?

Given that they can be used to deny you entry to your workplace and determine your entry to important government buildings, it's important to break it down.


What Are These Guns?

The infrared thermometer works using an infrared sensor. The sensor measures surface temperature from a distance without touching the skin.

A basic model measures the temperature by pointing over the central forehead. You have to hold it approximately 3 cm from the body surface. According to Sciencing,

"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 thermometer’s internal software will calibrate taking into account the room temperature, and will give a temperature value approximately equivalent to oral temperature.

Ear thermometers used on babies and toddlers? Those are infrared.


Do They Work?

Ineffective. That's how most experts have described it. I got a range of responses from people I reached out to. Some said the thermometer shows a temperature far less than the human body average, "It keeps showing 35 degree celsius. That's 2 degrees less than the average human temperature."

Another colleague was denied entry to the office gates as the guard declared her temperature was 3 degrees over normal. Except she felt fine.

The infrared thermometer measures the heat emanating from the surface of a person's body. If it is not held close enough to a persons forehead, it would give very low readings.

"I get different reports. Sometimes 92 or 89 and I should be dead!," said one amused doctor when I spoke with him, about a gun deployed outside his hospital.

Alternately, if it is too close, it will give off a high temperature reading.

"The gun showed 41 degree celsius and I felt fine," said another colleague.

Environment matters. So if the road is too dusty, the heat is too high (hello Delhi!), or if you have taken a medication to suppress the fever, it won't work.

"Many folks coming in from abroad would pop a Paracetamol so their temperature is suppressed," said a senior internal medicine doctor from Delhi.

What if I have been running to catch my flight? Or sitting inside a hot car in Delhi when it is 45 degrees outside? Yes, the reading can be very wrong.

"Some of these have been found to be really low quality. And on opening these a chip with three fixed reads is found. A sensitive thermometer like this gun should actually show a higher temperature if you are coming from outside from under the sun," says Dr Ashwini Setya, a senior gastroenterologist in Delhi.

A Chinese manufacturer told The New York Times in an interview that typically the gun was used indoors to check a baby's temperature. With the pandemic, the demand exploded. Now Amazon is selling it at a range of different costs.

Infrared Thermometers: Why They Are Unreliable in COVID Fight

Then there is the problem of calibrating the temperature. If the manufacturer has calibrated it wrong during manufacturing stage - it will show off a wrong reading.

According to an expert CNBC interviewed, the guns were originally designed to measure industrial machines. Using them to measure human temperature is just wrong.

The more reliable ones will have a range of 0.1 or 0.2 degree Celsius.

But no, it may still not alway catch most people - COVID symptoms show up several days after getting the virus. The fact that these guns were the primary source of spotting infections at airports, gives you an indication to why the infection spread to so far and wide.

(At The Quint, we are answerable only to our audience. Play an active role in shaping our journalism by becoming a member. Because the truth is worth it.)


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