smart window

-- electrochromic windows: Flip a switch and an electrochromic window can change from clear to fully darkened or any level of tint in-between.

-- liquid crystal windows

The technology works this way: two layers of film enclose a layer of tiny liquid crystals. This assembly is laminated between two pieces of heat-treated glass. Both faces of the film are covered with a transparent, electrically conductive metal coating. These conductive coatings are wired to a power supply.

-- thermochromic windows

As the prefix thermo- implies, heat causes thermochromic windows to alter their properties. In response to changes in the ambient temperature, clear thermochromic glazings becomes diffused.

-- photochromic windows