An ultra-miniaturized, low-cost, and maintenance-free chemical sensor is capable of continuously monitoring the concentration of specific volatile organic compound (VOC) vapors released from crop plants and green plants under distress from pests or disease. The sensor is based on micromechanical structures and relies on the mechanical actuation induced by the chemical interaction between the VOCs and materials in the microstructure to passively generate a wake-up bit when the concentration of VOCs exceeds a predetermined value. The sensor does not consume power while in standby mode (i.e., when certain VOC vapors are not present), and wirelessly communicates the location of impending outbreaks upon detection of a predetermined concentration of certain VOC vapors.