Today Internet of Things (IoT) technologies have been implemented in a broad spectrum of fields, serving and offering solutions to a wide range of problems. From smart home applications and elder care to industrial applications, Environmental monitoring, and Military applications, IoT has proven to be an invaluable tool for innovation. Financial analysis predicted that the Global IoT spending would grow 24% in 2021 and it is expected to further grow by 26.7% annually. Low-power wide-area network (LPWAN) technologies are the key enabler of the many faces of IoT technologies. LPWAN differentiates itself from traditional networks because it reduces costs and power consumption while increasing coverage. Its low-power performance makes it ideal for devices and sensors that need to have low battery consumption. Therefore, LPWAN stands out for its scalability while remaining really cost-efficient. LPWAN technologies are commonly selected for Early Warning Systems (EWS) networks for the prevention of natural disasters such as fire and flash floods. There are also networks that meet the needs of critical infrastructure such as nuclear power plants, electrical power plants, water supply plants, and more. For these reasons, it is imperative that the nodes that are used in critical infrastructures’ applications, must operate optimally, with high reliability and security. In this Ph.D. research the aim is to examine existing node development approaches for critical applications and to develop the methodology and tools for simulation and implementation of nodes that will integrate standards of reliability and secure operation.