Abstract: Pneumatic systems are important fluid power transmission mechanisms in industrial automation. They use compressed air to transfer energy and signals. However, leaks, which are mainly from seal failures or degrading pipelines, cause many problems. These include unstable pressure, equipment failures, and lower production quality. To offset leaks, air compressors often run harder, wasting energy and raising costs. So, timely and reliable leak detection is crucial for system reliability, cost savings, and safety. This review systematically examines current pneumatic leak detection technologies. First, it covers system basics and common leak points. Then, it evaluates detection methods, from traditional sensors to advanced intelligent algorithms. These are judged on accuracy, speed, and ability to handle environmental interference. The article also discusses challenges in complex environments, the shift toward remote monitoring via multi-sensor fusion, and the Industrial Internet of Things (IIoT). This review provides a foundation for selecting the most effective detection methods and offers key insights for intelligent, energy-saving pneumatic maintenance systems.