One way glass (window) reflective material?

I've got my birds returning this year & a nice feeder outside our kitchen window. Over time they seem to get a little more accepting of the activity in our home, but I was wondering what others do to help prevent indoor motion from scaring the birds at the feeders? I was thinking (actually, more hoping) that a material or substance was made that I could put on our kitchen window that would let us see the birds, but not let the birds see our movement indoors. Does anything like this exist? If not, what do others do to help prevent scaring the birds from indoor activity?

Yes Morph,I installed the mirror reflective film to observe our feathered friends last year' It not only helped save on our AC bill but cut the glare down as well.
I installed it on both of our entrance(outside glass)doors and then suspended a wad of white quilt batting(made a ball)on a string that will keep the birds from flying into the windows and get hurt' The string/ball catches the breeze and the movement prevents them from hitting the windows' HTH Sis'

Thanks, Sis! Do you remember if you found this at your local hardware store, or did you purchase it as a special item from a catalog or online? I'm just not sure where to begin my search... Thx :)

I found it at a home center called Sutherlands' It was near the paint dept if that helps,hope so'

It's called;PRIVACY MIRROR tm FILM. The rolls come in different sizes and there are special tools they recommend to help install the film'

Thanks so much. We used to have a Sutherlands. I'll check by my office in Cincinnati tomorrow to see if perhaps they have one there. Thanks for the details ~ it will help when I'm lost & a clerk asks me what I'm seeking ~ LOL...