Abstract: The Internet of Things (IoT) has revolutionized the way physical objects interact with digital systems, creating a seamlessly connected environment across various domains. This paper presents a comprehensive overview of modern IoT devices, focusing on their classification, core features, and emerging trends. It examines the technical architecture, connectivity protocols, sensing and communication capabilities, and application-specific design considerations of IoT devices. Furthermore, the study highlights their roles in smart homes, healthcare, agriculture, industrial automation, and environmental monitoring. The paper also addresses critical challenges such as interoperability, security, scalability, and energy efficiency. Finally, future research directions and technological advancements are discussed to provide a holistic understanding of the evolving landscape of IoT systems.