MODEL RELEASED. Strip thermometer. Boy using a strip thermometer to measure his temperature from his forehead. His temperature is displayed by the green area, which in this case shows 38 degrees Celsius. This indicates that he has a slight fever: normal body temperature is a degree lower than this. The cells in the strip each contain liquid crystals in a tight helix. The crystals are designed so that they expand and begin to reflect light at a specific activation temperature. Each cell's crystals have a slightly different activation temperature. Fevers can be reduced with drugs, but most are short-lived and harmless.