Infrared, just like any light ray, is an Electromagnetic Radiation with lower frequency (or longer wavelength).  Anything material above absolute zero (-273.15 degrees Celsius or 0 Kelvin) radiates in the infrared. Even ice emits infrared radiation.  Human eyes are design for visible light, but two species are known to detect IR: some rattlesnakes and beetles. Even though IR is not visible to the human eye, your skin can sense IR. When you can feel the warmth beside a campfire, you feel heat radiating from the fire.

The sensor in an IR thermometer collects a small amount of energy (usually 0.0001 watt) radiating from the target, generates an electrical signal and converts that signal into voltage output.  A CPU digitizes the signal by a 16bit Analog-to-Digital Converter, an Arithmetic Unit solves a temperature equation based on Planck's Radiation Law, compensates for the ambient temperature and emission which resulting in a temperature reading within a fraction of a second after you push the "read" button on the IR thermometer.

Many IR thermometers come with a laser pointer so you can clearly see where you are getting a reading from.  Always be sure to let anyone in the area know you are using the laser so you won't get any false positive photographs or video.  Also, we recommend an IR with a light source as it can be difficult and troublesome to shine a flashlight on the thermometer every time you want a reading.

Always get an average temperature in any location you are investigating.  Air, which is made up of oxygen and nitrogen molecules, does not emit infrared radiation.  However, you can aim an IR thermometer at anything having the SAME temperature as the air such as a leaf or grass (under sunshade) or indoors such as your desk, a piece of paper having the same temperature as the air and get a reading of the air temperature.  The key to measuring "air temperature" is to measure "anything that should have the same temperature as the air".