Real-time data are the life blood of the modern factory, and they are collected by smart sensors that act as the factory nervous system, enabling data processing for real-time decision-making, including predictive maintenance and process optimisation. This chapter explains how smart sensors help to realise the factories of the future. This work explores the various types of smart sensors, their functions, and the processes that constitute them on the technologies that support their functionalities. We define smart sensors and explain their importance in modern industries, especially for factors such as data privacy, sensor reliability, and compatibility with other systems.