How do Thermometer Guns Work?

You have probably come across one of these things in the past year.

Mansi Katarey


Photo by Anton on Unsplash

I know I have. During the COVID pandemic, these thermometer guns have become an essential part of our lives. But, how do they actually work? I see these guns everywhere, but I’ve always wondered how they work. How can something tell my temperature without actually coming in contact with me?

Here’s how:

Infrared Radiation

This is the backbone of the thermometer gun. If there is no infrared radiation, the thermometer simply will not work. You see, every object has atoms moving within it. Now, unless you’re in absolute zero temperature, you have atoms moving within you too. Right now. At this very second.

Hot atoms vs. cold atoms

Temperature and the speed at which these atoms move at are directly related. The faster the speed of the atoms, the higher the temperature. As they move faster, they emit more infrared radiation and eventually start to become visible (that’s if the object is really, really, REALLY hot.)

The atoms release energy in the form of infrared radiation, a type of electromagnetic radiation below the visible spectrum of light. What does that mean? The wavelength of this radiation is longer than those of visible light. That’s the reason we cannot see it with our eyes.

When metal glows red or even white, you can feel the heat emitted from it, even though we cannot see the wavelengths. The heat that we feel from the sun or the fireplace are some examples of infrared radiation. Infrared thermometers detect and measure this radiation.

A Black Body

Blackbody radiation refers to the spectrum of light emitted by any heated object. Some examples are incandescent light bulbs or the stars you see on a clear night. A Blackbody absorbs all incoming radiation and radiates the maximum amount of energy with each wavelength. The spectral intensity of blackbody radiation peaks at a frequency that increases with the temperature of the emitting object.

In simpler words, a blackbody is an object that absorbs all radiation, visible light, infrared light, ultraviolet light, that falls on it.

To read more about the concept of Black Body, check out this Britannica article.

Inside a Standard Infrared Thermometer

A Circuit Board

The top of the circuit board


The processor is the brain of the thermometer. Because of the size of the thermometer, typically, a microprocessor is used.


Power Supply

The power supply…well, you guessed it, it powers the thermometer. The type of battery can vary from thermometer to thermometer, but normally, a single 9V battery is used in standard thermometers.

The Power Supply

Sensor Assembly

This sensor is the main part of the thermometer. It reads the temperature by using an Infrared (IR) sensor.

IR Sensor


The display shows the temperature and other information. It is backlit by SMD LEDs.

The display is lit in green


The red laser helps aim the thermometer. It is activated when the trigger is pulled.

The thermometer itself is quite simple and uses basic principles of physics in order to work.

Are Thermometer Guns Accurate?

A normal thermometer measures your inside body temperature, but the guns measure your outside temperature, also known as your skin’s temperature. Your skin temperature can be affected by many different factors, including the time of day, after exercise and after spending time outside.

An experiment conducted by CityNews Toronto showed that after spending just five minutes under the sun, the thermometer guns displayed a temperature of 39.5℃, compared to 35.6℃ when sitting in the shade.

However, the thermometer put under the tongue was the only device that stayed consistent, at 36.3℃.

Check out this Youtube video to watch the full experiment!

I have experienced this first hand. Normally, when I leave the house, I splash my face with cold water. On those days, my temperature recorded by the temperature gun would be good enough for me to proceed into the store. However, one day, I had a lot of meetings and spent a lot of time in my room. My room gets hot very quickly, especially when the doors are closed. That same day, I forgot to splash my face with cold water before I left and suddenly, my temperature showed I had a fever. I couldn’t go inside, but when I came home and used my normal thermometer. I was just fine. My temperature recorded 37.1℃.

Thanks for reading! If you have any questions or want to chat further, contact me at:


or contact me through LinkedIn



Mansi Katarey

Passionate about AI and how it can solve problems around the world!