Occult hepatitis B virus infection (OBI), characterized by extremely low viral loads and the persistent intrahepatic presence of cccDNA, poses a profound challenge to global public health security. With a prevalence ranging from 0.06% to over 15% in different donor populations, OBI maintains a risk of transmission and can progress to hepatocellular carcinoma. Its prevention and control have long been limited by the sensitivity constraints of conventional detection methods, highlighting the urgent need for more sensitive diagnostic innovations. Emerging technologies offer distinct breakthroughs: ddPCR facilitates absolute quantification; CRISPR-Cas systems coupled with isothermal amplification enable rapid, point-of-care testing; third-generation sequencing resolves viral integration and mutations; and nanomaterials enhance the signal detection. This review synthesises advancements in OBI diagnostic technologies and provides a comparative overview of their strengths, limitations, and transfusion safety implications, as well as their potential applications in blood transfusion. Recommendations are also proposed to inform the advancement of OBI risk control in blood transfusion and to guide the development of novel diagnostic technologies, particularly relevant to regions with high HBV endemicity, such as China.