It doesn't just tell you if you had a brief, non-damaging high temperature, but tracks time as well as temperature, so that the result is a true indication of the temperature exposure. The label must be activated to start temperature monitoring.
Activation is done by hand instruments or automated machinery .
The labels are configured so that color producing dots are visible on the face of the label. Activation gives a green color to the dots by popping open internal pouches with fluids which mix to form an initial green color. The insert picture here shows how the internal mechanism works. A three dot label is one which has three pairs of pouches, all activated at once by the mechanism described above. The time for this color change depends on time and temperature.