Not long ago, there was some news release that a crowd weapon was developed that caused its target to become so hot that it was untouchable. Seemed to be a wide=area type application.
Silent Guardian. It heats a very thin layer of skin. When it hits you you feel pain, but it does not actually heat you up.
Heat stroke sometimes turns the victim’s skin bright red, and HS can come on very suddenly. But, a heart attack can give you a flushed face, too.