A No-Electronics Witness Label for Sealed Grain Stores: Integrating Moisture Exposure and Seal Failure on One Passive Card

A passive, no-electronics witness label for sealed grain bags and drums is designed and computed end to end. A latched humidity-indicating salt strip records peak moisture exposure and a throttled oxygen-sensitive dye spot integrates oxygen ingress from seal failure. Computed scenarios show each channel alone is blind to one failure case and the pair covers both: red in 0.66 days for grain sealed wet, red in 30.4 days for a breached seal in dry air, red in 0.76 days for a failed seal, and green through 90 days for an intact hermetic store. Reading bands are calibrated to grain moisture content and safe-storage days, unit cost is computed from a bill of materials, and the honest temperature range (15 to 35 degrees Celsius) and the directions of misleading behaviour outside it are stated in full. Design performance is SIMULATED, NOT MEASURED; nothing is described as built or hardware-tested.