It will not work behind a window. I'm pretty sure it uses PIR Motion sensor which requires change in temperature to detect motion. The camera will not be able to detect the motion through the window. As the previous reply also said, the night vision will most likely not work either as the infrared LED used for the night vision will simply reflect off the window and you will just have a bright/white reflection back at the camera.
If you really need a camera to work through a window you need what's called pixel based detection which the camera detects a change in the "scene" which it then decides if it's motion or not. With that being said though, more and more cams seem to be going the PIR route as even a leaf or tree moving in the wind can potentially change the "scene" and set off the camera if it's pixel detection based. Both detection methods have their merits I guess. Keep in mind again with either detection method the night vision will most likely not work through glass as you will get a reflection.
