This work presents a fully customized Bluetooth Low Energy (BLE) beacon system, developed using the Zephyr real-time operating system (RTOS). The beacon broadcasts structured, application-specific data through the Manufacturer Specific Data field, enabling a level of customization not offered by standard BLE profiles. A cross-platform mobile application, built with Flutter, has been designed to detect and interpret these customized signals in real time, providing a clear and interactive representation of the transmitted data. The complete system offers a lightweight, low-cost, and adaptable alternative to commercial solutions, particularly suitable for context-aware environments, smart infrastructures, and experimental research. The proposed architecture bridges embedded BLE development with mobile technologies, offering an open and scalable framework for customized wireless communication.