This review paper comprehensively examines state-of-the-art hydrogen sensors. The range of sensor types covered includes optical, mechanical, work function-based, interferometer, MOS, and electrochemical, by discussing their operating principles, material properties, and fabrication techniques. The literature survey traces developments from early piezoelectric devices to advanced micro-electro-mechanical systems (MEMS) and fibre optic sensors. Special emphasis is placed on critical performance indicators such as response time, sensitivity, operating temperature, and selectivity, which are crucial for practical hydrogen detection. In the conclusion, a comparative analysis highlights the advantages and limitations of each sensor type, offering insights into their suitability for different operational environments and potential future research directions. Comprehensive comparisons are drawn to guide improvements and facilitate the integration of these sensors into emerging energy systems, thereby advancing safe and efficient hydrogen monitoring.