Anything above absolute zero emits InfraRed radiation.
IR thermometers are calibrated for a very small temperature window, compared to the span of what is available. From low temps to high temps, many models are available. Many operate at a specific wavelength due to spectral windows on their transducers that make the unit very application specific.
A good IR thermometer,correctly factory calibrated, should be left alone, and will remain deadly accurate for years. If one thinks one's reading is off the mark, think about emissivity factor. Do not ever blame your instrument. Operator error is often (nearly always)the case. Calibrated thermo-couples are always nice to have around to verify your IR Thermometer reading capability.
That is, if one buys a reputable instrument to begin with.