Plant electrical signals are fast electrophysiological responses to environmental stimuli, physiological regulation and stress. Because they often change before visible symptoms appear, they are attractive indicators for early plant-health monitoring and for sensing in precision agriculture. Research in this area has moved from recording single action potentials to analyzing the plant electrome, and now draws on flexible wearable electrodes, implantable and electrochemical sensors, machine learning, multi-source data fusion and edge-cloud computing. This review follows the technical chain from mechanism to application. We first summarize the physiological basis of the main signal types and h... More >