Technological advancements integrate diverse sen-sors and actuators into daily life. Existing research mainly covers compatible, homogeneous, or extensively modified Wireless Sensor and Actuator Networks (WSANs) devices, leaving the integration of varied WSAN devices under-explored. To address these challenges, we introduce a novel concept of modularity in WSAN devices. Then, the Ease of Access (EoA) design model is presented for a modular WSAN (m-WSAN) system architecture by leveraging pervasive communication and distributed system design. The EoA design model provides a comprehensive method for categorizing and integrating distinct WSAN devices. It offers a blockchain-based WSAN service model for smooth device communication and collaboration. The design feasibility of such a system is validated by creating an m-WSAN system by integrating four distinct robotic systems and testing the designed network system to provide various operational services. The results demonstrate that any device can be added or removed from the m-WSAN system seamlessly without compromising the network system's integrity. Furthermore, this study lays the foundation for designing a modular robotic system comprising various sensor and actuator modules, each contributing distinct functional capabilities to the overall robotic system. This approach offers a flexible, scalable network for integrating diverse robotic devices, enhancing automation, and operational efficiency.