In this work, 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole (AHMT) was pre-doped into agarose hydrogels; consequently, sustained hydrogel systems with modulated release performance were constructed for simple operation and recyclability in point-of-care detection of formaldehyde (FA). With the increase in FA concentrations, the absorbance response of the supernatant solutions showed linear relationships and the color of the reaction mixtures gradually increased. The detection limit was calculated to be 0.013 μg mL-1. To verify its practical application, a simple, rapid and low-cost FA detection platform was built on the basis of the optimized conditions, and the method shows the merits of simplicity, high sensitivity and selectivity. More importantly, the developed hydrogels are recyclable and can be used at least five times without any loss in sensing performance. Significantly, the sensory hydrogels can be employed by non-skilled people for monitoring food safety and applied for the practical detection of FA in foods.