How do infrared pyrometers measure temperature?

Infrared (IR) pyrometers measure temperature by detecting thermal radiation emitted by objects. All bodies above absolute zero emit infrared radiation with intensity proportional to T^4 (Stefan-Boltzmann law). IR sensors use thermopiles or photodetectors to measure radiation intensity and calculate temperature. Emissivity setting is critical for accuracy; shiny/reflective surfaces require correction. Non-contact measurement enables moving targets, high temperatures, and hazardous environments.