This is kind of a joke mod. I've been enjoying it myself, but I imagine the novelty will eventually wear off.
In the process of experimenting with modifications to the analysis visor for an upcoming mod, I tried a very extreme color filter and kind of liked the result. It reminds me of the heat vision visor used by the alien hunter in Predator.
Just to be absolutely clear, let me state: this is only an aesthetic mod. It in no way functions like an actual heat sensor in-game. It simply alters the color palette you view the world through.
Stick in in your MODS folder.
1.0 - Release!