I can guess temps with my hand and get pretty close so I will not say that it cannot be done but I have a lot of animals and have been keeping reptiles for a long time. I always back my guess up with a shot from a heat gun. You need to remember that what feels warm to you is hot for a ball python. My animals run external body temperatures around the 84 to 86 degree range. Human body temperature is 98.6. So if something feels even slightly warm to you it is probably too hot for a ball python.