I used a cheap infrared non-contact thermometer to "zap" the temperature readings of my brake discs. Left front was 40 degrees warmer than the others after a short drive. I had suspected a warped rotor (death wobble when braking at 55).

Sure enough, found partial stuck caliper piston on inboard side, brake pad thin on that side from too much wear, and replaced the warped rotor.

I would guess that if a rotor is making more contact than it should, it would be warmer than one on the other side of the car. All that friction has to go somewhere.