AbstractEndowed with rich terminal groups, good electrical conductivity, and controllable structure, transition metal carbides/nitrides (MXenes) have attracted extensive attention for potential application in gas sensor, but long‐standing challenges of the MXenes (titanium carbide as the representative) are their limited selectivity and sensitivity. Herein, a high‐active double transition‐metal titanium molybdenum carbide (Mo₂TiC₂T_x) with superstrong surface adsorption (−3.12 eV) for NO₂ gas molecule is proposed, and it is further coupled with molybdenum disulfide (MoS₂) by interface modulation to construct an edge‐enriched heterostructure. Due to the synergistic effect of strong adsorption, rich adsorption sites, and coupling interface of Mo₂TiC₂T_x/MoS₂ composite, the as‐fabricated Mo₂TiC₂T_x/MoS₂ gas sensor exhibits an outstanding response toward NO₂ with high selectivity against various interference gases, which is well supported by density functional theory calculations. Meanwhile, the sensor exhibits a sensitivity of 7.36% ppm⁻¹, detection limit of 2.5 ppb, and reversibility at room temperature. A portable, wireless NO₂ monitoring system is demonstrated for gas leakage searching and dangerous warning based on Mo₂TiC₂T_x/MoS₂ gas sensor. This work facilitates the gas sensing application of MXenes, and provides an avenue for the development of wireless sensing system in environmental monitoring and safety assurance.