AbstractMetal halide perovskites (MHPs) have attracted significant attention owing to their simple manufacturing process and unique optoelectronic properties. Their reversible electrical or optical property changes in response to oxidizing or reducing environments make them prospective materials for gas detection technologies. Despite advancements in perovskite‐based sensor research, the mechanisms behind perovskite‐gas interactions, vital for sensor performance, are still inconclusive. This work presents the first evaluation of the sensing performance and long‐term stability of MHPs, considering factors such as halide composition variation and Mn doping levels. The research reveals a clear correlation between halide composition and sensing behavior, with Br‐rich sensors displaying a p‐type response to O3 gas, while Cl‐rich counterparts exhibit n‐type sensing behavior. Notably, Mn‐doping significantly enhances O3 sensing performance by facilitating the gas adsorption process, as supported by both atomistic simulations and experimental evidence. Long‐term evaluation of the sensors provides valuable insights into evolving sensing behaviors, highlighting the impact of dynamic instabilities over time. Overall, this research offers insights into optimal halide combination and Mn‐doping levels, representing a significant step forward in engineering room temperature perovskite‐based gas sensors that are not only low‐cost and high‐performing but also durable, marking a new era in sensor technology.