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We have developed a second-generation detection tube for colorimetric and fluorescence detection of phosgene and diphosgene in air. The tube is packed with pellets made of a mixture of microcrystalline cellulose and magnesium aluminum metasilicate treated with a suitable monoterpene (camphor, menthol) to increase porosity and specific surface area. We impregnated the pellets with a specific <i>o</i>-phenylenediamine-pyronin (PY-OPD) based reagent. The detector with this novel indication charge enables phosgene or diphosgene to be selectively and sensitively detected at concentrations lower than as would those posing acute health risk. Owing to the analytical colorimetric and, at the same time, fluorescence signal, the detector is very robust while featuring good sensitivity and variability. The colorimetric limits of detection were 0.3 mg/m³ (tristimulus colorimeter), resp. 5 mg/m³ (with the naked eye), fluorescence detection limits of 0.3 mg/m³ (with the naked eye), all at an air sample volume of 1 dm³. The response was practically immediate, acid vapors and gases, or diethyl chlorophosphate as a simulant of nerve warfare chemical agents, were disruptive.