In the recent years, large improvement is being achieved in the area of decontamination by fog of environmental pollution caused by natural and industrial disasters or attacks with biological, chemical, nuclear weapons of mass destruction. Basic to this technique is the performance of sensors for the existence of pollution and fog in the environment. This article is going to present a small-size and relatively inexpensive instrument, developed by us, which purpose will be to alert the occurrence of visible pollution in air or mist. In that way, it can be controlled, too, whether the cleaning mist has reached all areas. It is possible, that this equipment would assess the density of fog. It works in the infrared spectral region.