Hi,
I was kidding when i said "breed touch monkeys", and what i meant was genetically altering some monkey species to be able to discern temperatures more accurately and repeatable than a human can.
Sure, we as humans need to be able to tell when something is hot, but we dont need to be able to tell when something is 100 degrees C by touch.
Another technique is used in ceramic firing ovens. They use a piece of material that melts at a known temperature and deforms significantly so when it deforms it's done. For our purposes maybe some hot glue on the top of the device would tell the story. A little 'cone' of hot glue would deform once it got hot. Alternately, some of that low temp poly plastic...that stuff melts around 160 F i think so that would tell when it got pretty hot but not really really hot.
Also, how about a piece of temperature sensitive liquid crystal? Turns to a different color when it reaches a fairly precise temperature.