I'm working on a software that measures the facial skin temperature, a kind of 'fever detector'; In order to test the software, I want to check if my detector correctly works with objects with temperatures around 37.5 - 39 C, but I cannot find a 'device' that can be used for such measurements. A kind of thermostat, but it should keep static temperature on its outer shell. I tried to use a cup with hot water, but its temperature is being decreasing too fast, I would like to have an object with static temperature. Any advices on which device or object can be used are highly appreciated.
PS Soldering iron and Curling Hair with adjustable temperatures are working in too high temperatures range.