The threshold, spectral and operational characteristics of the experimental samples for photoresistors, fabricated on the base of the chemically precipitated semi-conductive lead sulfide films doped with chlorine and bromine during synthesis, have been studied. The developed photoresistors have an anomalously low time constant of 13-40 mks at relatively high level of photoresponse that is 15-40 times lower than known commercial samples based on the lead sulfide films. This fact allows using these photoresistors for creation fast-acting detectors of open flame and other high-temperature sources.