Rapid and simple detection of pesticide residues on agricultural commodities is essential for ensuring food safety and monitoring compliance with maximum residue limits. The present study evaluated the efficacy of an insecticide–Residue Indicator Drop (i-RID) method based on changes in contact angle for rapid detection of insecticide residues on brinjal fruits. The i-RID response was assessed on fruits treated with different insecticides representing various formulations, including carbofuran 3 G, chlorpyriphos 20 EC, dimethoate 30 EC, fipronil 5 SC, profenofos 50 EC, spiromesifen 22.9 SC, thiamethoxam 25 WG and triazophos 40 EC. In the absence of detectable residue, the indicator drops remained relatively spherical with an obtuse contact angle, whereas in the presence of insecticide residues, wetting of the fruit surface resulted in spreading and a significantly more acute contact angle. On the day of insecticide application, contact angles on treated fruits ranged from 54.75° ± 4.95° for profenofos 50 EC to 92.50° ± 4.29° for carbofuran 3 G, compared with approximately 133° on untreated control fruits. Significant differences in contact angle between treated and control fruits persisted for 5 days for carbofuran 3 G, chlorpyriphos 20 EC, dimethoate 30 EC, spiromesifen 22.9 SC, thiamethoxam 25 WG and triazophos 40 EC, while the response persisted up to 6 days for fipronil 5 SC and 7 days for profenofos 50 EC. The results demonstrated a clear and visually measurable difference between residue-bearing and untreated fruit surfaces. Thus, the i-RID method provides a rapid, simple and potentially field-applicable approach for preliminary screening of insecticide residues on brinjal fruits without requiring sophisticated analytical instrumentation. Further validation against conventional chromatographic residue-analysis methods would strengthen its applicability as a rapid residue-screening tool.