[@Zardoric] I did answer that question before, but here you go. I call them Fog Detectors.

[quote=@Treue]
[@Empath] Very good question, my apologies for forgetting to put that in the OP. In the early days of the apocalypse, when the Fog first began to appear, devices similar to Geiger counters were produced to detect high concentrations of the Fog. As giant fuckoff monsters began to appear, these were refined to be able to determine the location of nearby carriers of the mutagen. Children of the Dark are carriers as well, on a smaller level, so these devices were brought back into use for the Military Police. They come in many convenient forms! Accessorize.
[/quote]

More specifically, CotD can be detected by these up to three meters away.