Lead-free perovskites are promising for photodetector applications due to their excellent optoelectronic properties and low toxicity. However, the performance of perovskite-based photodetectors is often limited by defects in the films, leading to non-radiative recombination and reducing carrier mobility. In this work, we report the significant performance enhancement of CsBi₃I₁₀ perovskite photodetectors through Mn doping. Mn-doped CsBi₃I₁₀ films were prepared in an air environment, which still shows good stability. Structural and photoelectronic characterizations confirm that Mn doping effectively passivates defects, suppresses non-radiative recombination, and reduces the dark current. Furthermore, this doping strategy leads to a remarkably weak light detection feature and high reproducibility of the photodetectors. The optimized device achieves a responsivity of 1.11 A/W, a specific detectivity of 1.62 × 10¹² Jones, a fast response time of 4.53 (rise) and 1.47 μs (decay) under 650 nm illumination. Considering its special response spectrum and fast response under low-light conditions, a blood oxygen saturation monitoring system was successfully built on the Mn-doped CsBi₃I₁₀ perovskite, achieving high sensitivity. This work not only demonstrates an effective doping strategy for improving the performance of lead-free perovskite photodetectors but also highlights their potential as low-toxicity candidates for wearable health monitoring.