I have noticed some windows have a small sticker looking thing on them with a wire attached. I once asked someone what it was and he said it was a vibration thing to make it impossible to get a read on the conversation from the vibrations of the glass. You need some type of laser device to do this, but apparently such things exist.

In theory you could be ten miles away as long as you had a direct line of sight at the window.

I wonder if you put a popcorn popper next to the window it would mask your conversations? If not then at least you would have popcorn to munch while you were being snooped on.