Indonesia, located in the Pacific Ring of Fire, faces frequent seismic activity, posing significant risks to urban areas. Existing seismic monitoring systems are costly, require complex installation, and have limited real-time data transmission capabilities. This research aims to design a portable seismic instrument using the LSM303 sensor, integrating accelerometer and magnetometer functionalities for real-time monitoring of peak ground acceleration and magnetic anomalies related to seismic activity. The research employs a systematic approach encompassing hardware and software development, IoT integration for real-time data communication, and prototype testing. The device, characterized by its compact design, affordability, and ease of installation, transmits real-time data to a database and delivers notifications through a mobile application. Results indicate that the instrument effectively detects seismic activity and magnetic anomalies, addressing the limitations of conventional systems. It offers potential for integration into smart city infrastructures, enhancing disaster preparedness and response in urban environments. However, further validation under real-world seismic conditions is essential to ensure optimal accuracy and reliability. This study contributes to the development of accessible, scalable, and efficient earthquake monitoring systems, offering a significant improvement in early warning capabilities and public safety.