Electrochromic smart windows are valuable for green buildings, but conventional devices need external biases to operate - causing additional energy consumption. Now, in the journal Nature Communications, researchers from Singapore’s Nanyang Technological University report a self-powered electrochromic window, which can also be used as a self-rechargeable battery. They used aluminium to reduce Prussian blue (PB, blue in color) to Prussian white (PW, colorless) in potassium chloride electrolyte - producing a device capable of self-bleaching. The device can be self-recovered (gaining blue appearance again) by simply disconnecting the aluminium and PB electrodes, which is due to the spontaneous oxidation of PW to PB by the dissolved oxygen in aqueous solution. The self-operated bleaching and coloration suggest the self-rechargeable transparent battery function of the device. This video demonstrates the self-bleaching (discharging) of the self-powered electrochromic device by connecting the PB electrode and aluminium electrode.