<p>Hydrogen sulfide (H₂S) is a characteristic biomarker for early pork spoilage. However, existing rapid detection methods often rely on expensive instrumentation, complex signal processing, or are susceptible to environmental interference (e.g., humidity), limiting their practical application. Here, we report a novel, humidity-robust colorimetric hydrogel sensor that addresses these challenges. The key novelty lies in a synergistic composite design: a sodium alginate-chitosan (SA-CS) polyelectrolyte network is used to stably immobilize Pb²⁺ via dual anchoring (-COO⁻ and -NH₂), forming a Pb²⁺-SA-CS sensing hydrogel. Unlike conventional organic-dye-based sensors that suffer from dye leaching and instability, this Pb²⁺-based system provides a specific, stable, and interference-resistant chromogenic reaction. Furthermore, the hydrogel’s intrinsic high water content eliminates the need for hydrophobic pretreatment, enabling direct, stable operation in the high-humidity environment of packaged pork. Using a smartphone to capture color changes and quantify them via Euclidean distance, the sensor achieves a low detection limit of 0.82&#xa0;ppm for H₂S, an 8&#xa0;min response time, and good selectivity. In a 7-day pork spoilage simulation (4&#xa0;°C), the hydrogel exhibited a clear color transition from pale white to dark brown, which strongly correlated with total volatile basic nitrogen (TVB-N) values (R² = 0.9819), accurately tracking the spoilage process. Practical significance: This work provides a low-cost, portable, user-friendly, and humidity-robust visual sensor. By enabling real-time, non-destructive pork freshness monitoring without external power or complex equipment, it holds significant promise for intelligent food safety supervision at the consumer and supply chain level.</p>