The demand for compact and low-power sensor nodes (SNs) as wearable devices has increased significantly as they contribute significantly to the monitoring of people's health status, providing valuable information for the treatment of various diseases. To address this issue for epilepsy diagnosis, we propose an energy-efficient SN design. The SN incorporates both accelerometer and gyroscope sensors monitoring movements and can be easily attached to an electromyography (EMG) sensor monitoring muscle activities. An internal contact socket allows seamless integration of both devices. The designed system has been tested on a healthy subject and has demonstrated high-quality data measurement. The SN uses low-power Bluetooth 5.0 to communicate with the mobile application, which is designed to modify the built-in sensor parameters and monitor sensor output in real-time. It has an average current consumption of 14.3 mA. In addition, all data from the developed system can be stored on an attached SD card, providing a reliable storage solution.