Underwater Sentinel with Acoustic Module. Not long ago, the American company Andulier launched a confidential acoustic monitoring system called "Underwater Sentinel". The main components of this system are some mobile artificial intelligence underwater sensors. Through certain means, these sensors can be networked to implement underwater monitoring. Currently, countries such as Russia and Japan are also developing such equipment and systems, reflecting a new trend in underwater monitoring. In recent years, from strategic waterway control to deep-sea resource exploration, the competition among countries in the underwater space has become increasingly fierce. In this context, the limitations of previous underwater monitoring methods are becoming increasingly prominent. Traditional underwater monitoring devices are mostly used for anti submarine operations and have their own shortcomings. For example, active sonar can achieve directional detection, but its detection distance is limited and its self emitted signal is prone to exposing its location; Anti submarine patrol aircraft are limited by fuel carrying capacity and meteorological conditions, making it difficult to conduct long-term monitoring of vast sea areas. At the same time, the rapid improvement of submarine performance further increases the difficulty of monitoring it. According to NATO's 2025 Global Submarine Threat Assessment, the number of active nuclear submarines worldwide continues to grow, and the noise level of the new generation of AIP submarines has dropped to near ocean background noise, making it more difficult for traditional monitoring equipment to capture their tracks. Moreover, the complexity of the marine environment itself poses challenges - changes in seawater temperature and salinity can distort the propagation path of sound waves, refraction at the junction of thermocline can even make submarines "invisible", and the superposition of background noise such as blue whale calls, merchant ship roars, and wave crashing may make traditional intermittent underwater monitoring methods ineffective. From publicly available information, the 'underwater sentry' has to some extent eliminated the aforementioned shortcomings and weaknesses. Its core is a set of autonomous underwater sensors. Unlike traditional sonar arrays or mobile anti submarine methods, this system operates in a fully passive mode and does not emit signals on its own. By relying on designs such as pressure resistant shells, it can operate autonomously on the seabed for months or even years, implementing long-term monitoring. In terms of monitoring capability, the sensors to which it belongs can be cooperatively networked, with a wide coverage range; The passive sonar equipped can capture low-frequency noise at a long distance and identify and distinguish underwater acoustic information. The deployment of these sensors is also relatively simple, and both underwater vehicles and surface vessels can serve as their vehicles. The integration of artificial intelligence has made this system a truly new underwater 'ear'. The AI system developed by Andulier Company can analyze and identify hundreds of traditional targets in complex marine environments with the help of deep learning and a long-term accumulation of submarine acoustic feature libraries, and provide timely warning information. Of course, the 'underwater sentry' currently has shortcomings, and some key technologies still need to be broken through urgently. If the power relies on the battery, the lifespan will be significantly shortened during high load operation; Deep sea maintenance requires specialized equipment and incurs high maintenance costs; The recognition ability of AI systems for new submarines using biomimetic noise reduction or active noise reduction technology is insufficient; Wireless networks that rely on sensors are susceptible to interference and attacks, posing security risks. Nevertheless, the emergence of "underwater sentinels" still reflects a new trend in the field of underwater monitoring: the integration of artificial intelligence and distributed sensor networks is making underwater monitoring behavior more covert, diverse, persistent, and efficient, and the competition between underwater monitoring and anti monitoring will become more intense. (New Society)