An IR thermometer detects the temperature of a spot located some distance from the sensor. The distance may be a few inches or a few feet. The optics of the sensor will determine the spot size that will be measured at a given distance, called the distance to spot ratio.

When measuring, the temperature emission of a large spot may not be uniform. Many instruments will measure the maximum, minimum and average temperatures of the region. These are called the measuring modes.

The emissivity is the efficiency with which a surface radiates the IR waves. Perfect radiation has an emissivity of 1.0 and is called a blackbody.

The emissivity of the object to be measured has to be entered in the thermometer to get an accurate reading. In most models it can be entered from the readout which has either three or four LEDs. Memory storage is available on many models as are USB and Ethernet outputs.

An important feature that is standard on most instruments is a laser pointer. This assures that the correct point is measured particularly with instruments with a large spot ratio.

The products listed here have technical features that put their price above $1000. Simple instruments starting in the $100 range are available from some of the manufacturers.