Methyl jasmonate (MeJa), a vital phytohormone plays a crucial role in plant growth and defense mechanisms to protect plants against biotic as well as abiotic stresses. Therefore, easy and accurate detection of MeJa in a user-friendly, comprehensive manner by farmers is of utmost significance in agriculture. This work reports a first of its kind ultra-low-cost pyrite FeS2 based smart sensor on flexible paper substrate for determination of MeJa with a detection limit of 0.2 mM,excellent selectivity, reproducibility, and high sensitivity. Firstly, the electrochemical sensor based on pyrite FeS2 exhibited a sensitivity of 412.2 μA.mM-1.cm-2 (R2 = 0.971) in the physiologically relevant range of 0.25-1.5mM and 230.4 μA.mM-1.cm-2 (R2 = 0.990) in the region of 1.5iV4.5mMof MeJa. This significant enhancement in the analytical performances of the FeS2 sensor can be ascribed to the high conductivity of the pyrite FeS2, large surface area resulting from its microspheres like morphology comprising of interwoven vertically grown nano-sheets and the presence of defects in FeS2 structure. Further, wireless monitoring of MeJa was achieved by direct growth of pyrite FeS2 on cellulose paper by hydrothermal method and its integration with the microcontroller, from where the data collected was transported to a smartphone via Bluetooth, thus facilitating remote sensing. The pyrite FeS2 based disposable, chemi-resistive sensor displayed limit of detection of 0.68mMand excellent sensitivity of 12.24 ± 1.4%mM-1 (R2 = 0.96) in the range of 1-2.5mM of MeJa. The development of such lowcost nano-material based disposable sensor is a huge step ahead in the fabrication of affordable, nextgeneration lab-on-chip devices for analytical applications. © 2020 IOP Publishing Ltd.