Smart sensor technologies and wearable Internet of Things (IoT) devices are transforming medical treatment by continuously monitoring physical and biological parameters with non-invasive approaches. These sensors are built into wearable devices like smart watches and clothes to help collect, process, and transmit vital sign data and information for diagnosis. In this chapter, we discuss the development and application of smart sensors and wearable IoT devices, as well as their impact on medical services. We also describe in detail the functions of physical, chemical, and optical sensor types and their unique health monitoring functions. The integration of these sensors with IoT systems results in a connected health care ecosystem that increases real-time data exchange and analysis to improve patient outcomes and clinical efficiency. Advances in sensor fusion technology are discussed, demonstrating how data from various sensors can be integrated to improve health information accuracy and dependability. We additionally address issues related to applying these technologies to key challenges, such as security risks and data privacy. Block chain technology is proposed as a solution to these challenges, with the Internet of Medical Things (IoMT) providing strong data integrity and accountability. Furthermore, we underline the relevance of ethical considerations and regulatory compliance in preserving trust and ensuring the safe and effective deployment of smart sensor technologies and wearable IoT devices in healthcare. Despite these challenges, the potential for these technologies to support data-driven medical practices, enhance patient care, lower medical costs, and increase access to health services, is a promising possibility.