Ultraviolet-infrared detectors respond to flaming fires emitting light in both the ultraviolet and infrared portion of the light spectrum. UV-IR detectors require both the uv and the ir sensor to alarm simultaneously. This makes them very resistant to false alarms including welding, x-rays, lightning, artificial lighting and interrupted hot body radiation, because while there are sources in the environment other than fire that will cause the UV or IR sensors to false alarm, they have virtually none of these sources in common.