One of the multiple approaches employed to monitor older people and check their health status is the use of the Hidden Markov Models (HMM), a statistical model that uses observable facts to model hidden events. Chapter One present a systematic review of using the Prisma Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) that was updated in 2020 to incorporate the latest technologies and techniques. The review aims to establish the state of the art of the subject and presents as a conclusion how the HMM has been used and which are the open issues that need deeper research or new development to get new insights. To achieve this aim, the PRISMA methodology is carried out on Web of Science, PubMed, and Scopus. Chapter Two focuses on developing processes that provide tools (including soft and hard, analog and digital technologies) to any type of population, to break the inequality gaps in the context of the 4th industrial revolution. Chapter Three provides an overview, applications and challenges of VLC ODFM (orthogonal frequency division multiplexing) systems. In Chapter Four, the authors propose a low-cost, simple, and durable IoT-based system for the following two purposes: 1) predicting crops suitable for a given piece of land based on the soil parameters, namely, soil potential of Hydrogen (pH) and soil temperature and 2) monitoring and automating some of the recurrent processes, i.e., adding fertilizer such as Nitrogen, Phosphorous, and Potassium (NPK) and irrigation of the land. Chapter Five focuses on the effect of noise on the dynamics of natural processes. Chapter Six presents a study regarding the contribution of inrush current to the occurrence of mechanical fatigue in windings of a power transformer and, consequently, the impact of that phenomenon on the equipment's lifetime. Chapter Seven presents a design for short circuit withstand capability of a transformer. The short circuit test is carried out to verify the integrity of short circuits developed when short circuit current flows through the transformer. In the final chapter, the problem of initial orientation of strapdown navigation system on a movable base is solved using inertial measurements under the most general assumptions about the nature of random angular motion of the base. The solution to the problem is obtained in the form of an extended Kalman filter.