Thermal monocular are standard technological devices which detect very minute differences in the heat to produce an image.
Roughly, we know that monoculars are very much similar to a camera and an ocular gadget that uses the visible light in front of it to capture the scene but the difference here is, thermal monocular works by detecting the heat signatures using thermal imaging technology.
What is a Heat Signature?
Every object in the world emits radiations with various wavelengths but these radiations would differ from each other.
The humans and certain animals emit radiation in the range of 0.75 to 1000 microns which is very much similar to the wavelengths of the infrared radiations aka infrared signature (Check Wiki for a complete history of IR radiation).
This heat radiation from each object is called the heat signature.
Infrared radiation cannot be seen by the naked eye because of the ocular limitations of the human eye.
The IR radiations from various objects are captured by a sensitive thermal imaging sensor that is placed inside the monocular and the images produced by these monoculars usually are grayscale in nature.
The object which emits a good amount of heat appears to be white on the screen while the cold objects appear to be black.
Thermal imaging is being used to minimize the spread of Coronavirus (COVID-19) by detecting body temperature that is using their heat signature.
Yes, Infrared thermography can able to detect the elevated body temperature that may be a cause of fever.
In that case, using IR radiation as a diagnostic tool to inspect people for fever may minimize viral diseases such as COVID-19 (coronavirus), SARS, and other infections from spreading.
Because fever or raising body temperature is a definite symptom of severe flu and bacterial infections.
Death and people got infected to COVID-19 massively increases worldwide, so public health ministries are in the search to find a better way that is reliable, easy, fast, and contactless to contain the COVID infections.
Where they found thermal screening, it is the best option as of now when appropriately used.
Thermal detection is now used around the world in all the public places and transport areas to detect the temperature change in civic groups.