Temperature is basically the measurement of how hot or cold something is, and it is one of the fundamental entities in any kind of process control. Temperature is also a measure of the average kinetic energy of particles in a system. Adding heat to a system increases the kinetic energy of its particles and hence an increase in the temperature of the system. The body temperature of a human being is controlled by the brain and is around 35.5 degrees C-37.7 degrees C. Large changes in the body temperature are usually an indication of an illness. This paper describes the development of a microcontroller based device for measuring and logging the body temperature on an SD card continuously. The collected data can then be analysed statistically to determine the state of the patient.