I have been working on the same question for my own master bath. (But you know architect's houses are like the shoe maker's children...so I have not done it yet!)
But I have 2 ideas:
- One way glass. If you google 'public toilet of one way glass' you can see a really great example. Basically the window will look like a mirror on the outside and you will be able to see through it on the inside. Cool!
- Switch-able glass...or Smart glass. There are many manufacturers of this sort of glass - I would ask your local glass or window people. Basically this is clear glass that is turned translucent by the flip of an electrical switch. So maybe you have a switch within reach of your shower so if you see someone outside you could quickly flip the switch.
One problem with both ideas is that they have to be turned into something like an exterior window (meaning weather proof and perhaps somewhat energy efficient. )
- I am told by my local window guy that you could make a double pane window using normal glass per window manufacturer on the outside and whatever glass you like on the inside.
- So I am confident that either would work.
Best of luck! I make no promises for cost!
Please post if you do either of these. I would love to know how it went.