What is thermal imaging?

Heat gives off infrared light, which is on the part of the electromagnetic spectrum that isn’t visible to the naked eye. A thermal (or infrared) imaging device translates thermal energy — that is, heat — into visible light. 

Thermal cameras take pictures of heat in the same way that your smartphone or camera takes pictures of visible light. Since thermal cameras ignore the visible light portion of the spectrum, their results aren’t hindered by solid obstacles like walls, roof beams, or bulky furniture.