Device for registration of temperature over an area by means of thermochromatic materials, which includes one, two or several layers (1, 3) with thermochromatical material, and one or several surrounding heat storing plastic layers (4, 6) that extend the reading time with maintained heat picture. In the case with several thermochromatic layers these preferably are of different termocromatical materials reacting at different temperatures and so chosen and so arranged that the termocromatic materials together constitute a scale of temperature areas. By means of a template the colors in the termocromatic layers can be interpreted to temperatures or temperature intervals and be noted.