I am retired LEO.
Unfortunately, I have to agree with some of the other posts here. At least back in my day the Kevlar was a superb insulator and reflector of body heat, no matter what the outside temp. By the end of the shift you were usually drenched in sweat under the vest. An additional heating pad would not work in this situation IMHO, at least not for the majority of LEO's (there is always the exception to the rule I suppose). I would guess that this would be far more useful for hunting in the fall, or snow mobile use, or Skiing...