Today, an increasing part of the modern way of life is based on the use of smart devices based on IoT technologies. These devices, through data collection, offer an unprecedented ability to manage our daily lives. One of the fastest growing areas of IoT applications is Sports, where smart devices provide us with a more interesting and personalized sports experience, while allowing us to constantly monitor our performance through commonly accepted metrics. However, the existing implementations have high costs and a limited range of possibilities, aiming to cover a specific type of exercises. In this Diploma Thesis we attempt the complete development and construction of a low-cost modular device, which will be the basis for the integration of a large number of sports exercises through a common interface. The development of this device includes the design of the hardware (PCB) based on the ESP32 microcontroller, the programming of the hardware through the Riot-os real-time operating system, the bridging of the communication between the device and the internet through a Raspberry Pi computer node using IoT protocols and build the original casing of the device with the help of 3D printing. Then follows the evaluation process of the device during which we make measurements related to its energy consumption and autonomy. Finally, we will try to integrate a number of sports applications that are found in research and commercial implementations of devices in order to explore the adaptive ability of our device.