>>>> How do they measure temperature, though? It seems to me that the temperature would govern the wavelength directly, not the intensity of the IR radiation. The intensity is related to the quantity of radiant heat, which would be a function of the surface that it was being radiated from, etc. So how does one get temperature from measuring the magnitude of the voltage generated on the sensor? It seems to me that this is like saying that you can sense color by measuring the amount of voltage generated by a solar cell. <<<<<<<< IMHO, the pyro sensors don't measure temperature, usually. The only example of temperature measurement given in this list was for an ear therometer. Well, if you stick it in your ear, the surface area is fixed and fills the aperture of the sensor hence the area of emission is not a factor. I'm not sure how the emissivity variable is eliminated, but in the far IR the emissivity of most things, except maybe metals, is high and doesn't vary much. John-