Increasing　voltage　levels　and　realizing　power-line　communications　are　important　parts　of　a　smart　grid,　and　because　of　this,　the　need　for　intelligent,　digital,　and　multi-functional　electronic　sensors　that　can　simultaneously　perform　the　functions　of　high-voltage　monitoring　and　carrier-signal　demodulation　in　a　power　transmission　system　is　urgent.　Inspired　by　the　operation　mode　of　light-emitting　diodes　(LEDs)　driven　by　triboelectric　nanogenerators　(TENGs),　we　propose　an　electrode-LED-electrode　structure,　namely,　LED-in-capacitors　(LIC),　for　high-voltage　monitoring　and　high-frequency　signal　demodulation.　We　demonstrate　that　the　proposed　LIC　can　sensitively　extract　the　high-voltage　amplitude　and　detect　the　harmonic　pollution　on　a　power　line　due　to　the　LIC＇s　being　highly　sensitive　to　the　rate　of　change　of　the　electric　potential.　We　build　a　one-dimensional　convolutional　neural　network　that　we　use　to　identify　successfully,　with　correct　rate　as　high　as　94.53%,　the　harmonic　pollution.　Additionally,　by　using　the　LIC,　we　are　able　to　demodulate　accurately　the　high-frequency　carrier　signals　transferred　in　the　high-voltage　line,　showing　that　the　LIC　has　promise　for　potential　applications　in　power-line　communications.　As　a　novel　type　of　electronic　device　derived　from　TENG-related　technology,　we　believe　the　LIC　can　provide　impetus　for　the　development　of　next-generation　high-voltage　technology.