Upcoming generation of smart windows requires simple design, fast stimulus response and cost-effective production. Aiming these features, we reported a new approach of switchable devices based on the thermosensitive polymer poly(N-vinylcaprolactam) (PNVCL) and facile assembly of the components (FTO layers and polymer). Its optical/color change from transparent to opaque is temperature-dependent and activated by induced Joule heating of conductive substrates. Therefore, the reported devices showed fast reversible response (less than 60 s) by small input power and adjustable opaqueness according to polymer concentration. In opposite to traditional electrochromic smart windows dependence of the kinetics charge-transfer reaction, the observed features are triggered by the thermodynamic mechanism of the reversible coil-globule transition from PNVCL suspension, which can lead to stable performance of the proposed device.