How do glass doors that frost when you lock them work?

Answer

Dear Ineke,

there are a number of ways these can work. One way is to process certain molecules in the glass in a layer or in microscopic droplets. These elongated molecules are randomly oriented and thus ensure that the light is scattered. In other words, the glass looks milky.
However, when an electric current is applied over the glass, these molecules, under the influence of that electric field, all start to orient themselves in parallel. As a result, the light is no longer scattered and the glass becomes transparent.

There is a system in the lock of the toilet door that turns off the power when you close the toilet door, and you have your privacy as long as the door is closed. When the door opens, the power is turned on again and the door is transparent again.

Regards,
Benjamin