The changes in physical environmental parameters have severe impacts on food safety and security. Therefore, it is important to understand micro-level physical parameter changes occurring inside food packages to ensure food safety and security. The emergence of smart packaging has helped to track and inform the specific changes such as a change in humidity, temperature, and pH taken place in the microenvironment in the food package. Moreover, these key physical parameters help determine the freshness of the food as well. Radio-frequency identification (RFID)-based sensors are an emerging technology that has been used in smart packaging to detect changes in the physical stimuli in order to determine food freshness. This review looks at the key environmental factors that are responsible for food safety and food freshness, the role of smart packaging with sensors that can measure changes in physical stimuli in the microclimate and the detailed review of RFID-based sensors used in smart packaging for food-freshness applications and their existing limitations.