The Testo 0646 3341 Testoterm Self-Adhesive Thermometer Strips, 399.2 to 500 °F, are thin temperature-sensitive pieces of film that change their color when the temperature exceeds a specific value. This makes them ideal for monitoring the temperature of products and processes where the temperature is not allowed to exceed a certain limit, i.e. for moving or small objects like circuit boards, for long-term monitoring of storage and transport temperatures, in laboratories, in automobile technology, in aviation and in astronautics.

The strips are peeled off and applied to the object you wish to measure. They have a temperature scale ranging from 399.2 to 500 °F, which is divided into little white boxes. As soon as a specific temperature has been exceeded, the strip changes color in the relevant boxes within 2 to 3 seconds.

When the strips change color, they do so irreversibly. When a certain temperature has been exceeded, the color does not change back again when the temperature returns to previous levels. This allows you to see that critical thresholds have been exceeded even when the temperatures have returned to the levels they were before the limit was reached. This makes them ideal for use in storage and transport.