Since the effectiveness of triboelectric charged surface being charged is strongly dependent on the surface adsorbed molecules, we show that the triboelectric nanogenerator, made of polyamide 6,6 (PA) film or polytetrafluoroethylene (PTFE) film, can serve as a self-powered active sensor for detecting water or ethanol in gas or liquid phase. The performance of the active sensors has been understood in reference to the levels of wettability of solid polymer surfaces. This new approach for sensing could be advantageous of simple fabrication, low-cost and easy application. The triboelectric nanogenerator, made of polyamide 6,6 (PA) film or polytetrafluoroethylene (PTFE) film, can serve as a self-powered active sensor for detecting water or ethanol in gas or liquid phase. The performance of the active sensors has been understood in reference to the levels of wettability of solid polymer surfaces. Display omitted •The TENG is made of polyamide 6,6 (PA) film or polytetrafluoroethylene (PTFE) film.•The TENG can serve as a self-powered active sensor for detecting water or ethanol in gas or liquid phase.•The performance of the active sensors has been understood in reference to the levels of wettability of solid polymer surfaces.