Chinese researchers have developed a highly sensitive magnetic sensor that could enable smartwatches to detect submarines at depths of up to 500 meters. The breakthrough, achieved by teams at the Hefei Institutes of Physical Science and the Ningbo Institute of Materials Technology and Engineering, utilizes Hall-effect technology. This innovation potentially allows for the creation of portable devices capable of identifying subtle magnetic anomalies indicative of underwater vessel presence. While currently a research development, the technology could eventually offer new capabilities for maritime surveillance and security. The sensor’s sensitivity marks a significant advancement over existing magnetic detection technologies. The team’s work represents a step toward integrating advanced submarine detection into everyday wearable technology, offering potential benefits for both civilian and military applications. This research highlights China’s growing capabilities in materials science and sensor development.