Biodots® (2) with instructions.
Biodots measure skin temperature. They change colors as your temperature changes.
They are used when you practice mindfulness, especially the autogenics training where you become aware of the heaviness and warmth of the limbs of your body as described by Dr. Jaime Carlo-Casellas on page 67 in his book, Mindfulness for the Common Man.
The Biodot may be placed anywhere preferably on the dominant hand, just above the webbing between the thumb and forefinger. Yet you may want to experiment with different locations to see if there are significantly different results between one hand and the other or on warmer spots such as the palm.