**4. Conclusions**

Temperature sensors are key elements in the development of new innovative technologies in actual areas such as wireless health care devices, robotics, smart manufacturing, and smart products. Polymer composite materials with PTC effect are smart materials, with intrinsically abilities of self-limitation of current/voltage and, on this basis, being able to function as smart temperature self-regulating heating elements or as smart fuses. The use of PTC materials as temperature sensors (thermometers) seems complicated by the important nonlinearity of the temperature dependence of the resistivity, but over quite wide ranges, for example, between the ambient temperature and the onset of the resistance steep rise before the critical temperature, the resistance—temperature signal is practically linear enabling the development of interesting applications such as interactive monitoring body temperature with wireless devices.

Conductive carbonaceous materials such as CB, graphite, graphene, CNT, and CF are intensively studied to obtain PTC or NTC resistive temperature sensors in efficient printing-based technologies, to obtain flexible or stretchable sensors, required by new technologies of sensing. The large number of articles published in recent years in relevant publications is a further proof of the topicality of this field.
