Methylammonium lead tri‐iodide (MAPbI3) hybrid perovskite powder is successfully synthesized using a two‐step antisolvent precipitation (TSAP) method. This MAPbI3 powder is compressed to make a pellet, on the surface of which is designed an ammonia sensor that operates at room temperature. The tetragonal structure and porous morphology with well‐connected perovskite grains of the pellet are studied using X‐ray diffraction and scanning electron microscopy techniques. This is the first report of air‐stable, substrate free, and robust ammonia sensors based on perovskite pellets based in which the perovskite powder is synthesized with an unreported TSAP method. Gas‐sensing measurements show responsivity of 200% in 0.3 s and excellent recovery in 3.6 s upon exposure to 10 ppm ammonia gas. The sensor shows excellent structural and morphological ammonia sensing reversibility. A MAPbI3 pellet stored in ambient air with a relative humidity of 20–45% exhibits a lifetime of 60 d. These results successfully demonstrate new insights for environmentally friendly low‐cost manufacturing of highly sensitive robust perovskite ammonia sensors.

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