Meet the Glass Apps self adhesive Smart Window Film: a solution that applies to any smooth glass surface and goes from clear to opaque. It has a simple on/off mode switch that allows you to use the film as an electronic blind to get some privacy when you need it. Here is how the PDLC technology works:
In clear mode an electrical current is passed through the PDLC (Polymer Dispersed Liquid Crystal) interlayer which aligns the microscopic crystals along a number of parallel axes, thus allowing vision through the glass.
These videos show this smart film in action:
The smart film is available in multiple shapes, sizes, and colors. You can find out more information about it here.