But if you stick your nose up to it and cup your hands around your eyes to shield out the light you *CAN* see through them. There is no such thing as one-way glass. In reality it's glass with a reflective component to it, when you are looking from the light side to the dark side all you get is the reflection as it's the brighter image. From the dark side to the light side the image coming through is the brighter one, that's what you see.

In a sense we have it on our house. It's not the glass itself but rather solar screens. They are a mesh that blocks 80% of the area, but the holes are small enough that if you're not up close you see through it anyway. During the day we can see out clearly (albeit with a tinge from the color of the screens) but it's impossible to see in--I've stripped her naked while we were a few feet from the patio door that doesn't even have curtains or blinds. At night, however, the situation reverses--it's impossible to see out unless we turn off all the lights.