The widespread application of pesticides in modern agriculture has raised significant concerns regarding their accumulation in food products and environmental matrices, posing substantial risks to human health and ecological systems. Conventional analytical methods for pesticide residue detection, including chromatographic techniques, are time-consuming, expensive, require sophisticated instrumentation, and are unsuitable for on-site real-time monitoring. Smart nano-sensor technologies have emerged as transformative solutions that enable automated, rapid, sensitive, and real-time detection of pesticide residues across diverse food and environmental samples. These advanced sensing platforms leverage the unique physicochemical properties of nanomaterials—including metal nanoparticles, carbon-based nanostructures, quantum dots, and hybrid nanomaterials—to achieve exceptional sensitivity with detection limits reaching parts per trillion levels. Integration with electrochemical, optical, and biosensing mechanisms provides versatile detection strategies tailored to specific pesticide classes and matrices. The incorporation of automation through microfluidic systems, internet of things (IoT) connectivity, wireless sensor networks, and artificial intelligence-driven data analytics facilitates continuous, remote, and intelligent monitoring capabilities. Applications span food safety assurance in fruits, vegetables, grains, and processed products, as well as environmental surveillance of water bodies, agricultural soils, and atmospheric contamination. Despite remarkable progress, challenges including sensor stability, matrix interference, standardization, regulatory acceptance, and scalability for field deployment require continued innovation. This comprehensive review examines the state-of-the-art smart nano-sensor technologies for pesticide residue detection, their underlying mechanisms, automation strategies, practical applications, and future directions toward achieving comprehensive food and environmental safety monitoring systems.