Honeywell FSL100 flame detectors monitor hazardous areas for invisible infrared or ultraviolet light that occurs outside the frequency range of visible flames. The FSL100 series detects both hydrocarbon and non-hydrocarbon flaming fires to address a wide range of fire protection applications both indoors and outdoors. These units resist the influence of direct and reflected sunlight, and artificial light sources such as fluorescent bulbs or halogen lamps. They can even successfully monitor an area affected by smoke, dust, or vapor .

The FSL100-UV ultraviolet flame detector is best suited for indoor applications such as fume hoods and hydrogen storage areas, and as an effective solution for materials burning with low temperatures, such as sulfur. It alarms for fires caused by heavy hydrocarbons (wood, paper, petroleum), light hydrocarbons (methanol and methane), and hydrogen .

The FSL100-UVIR ultraviolet and infrared flame detector uses analysis of the flame-flicker frequency for improved false alarm rejection. Its dual sensing methodology enables a wide range of hydrocarbon and non-hydrocarbon fires to be effectively detected. This unit resists arcs and electric discharges and remains unaffected by radiation from electric welding stationed at least ten feet away .

The FSL100-IR3 triple infrared flame detector is particularly suited to liquid hydrocarbon, dirty fires, or fires that emit large amounts of smoke. It uses analysis of the flame flicker-frequency for improved false alarm rejection, resists arcs and electric discharges, and is less affected by window contamination or smoky fires. All models feature a robust GRP housing, 90° cone of vision, 4-20mA and relay outputs, and automatic/manual self-test .