Battery cameras use PIR (passive infrared) motion detection, an energy-efficient (saving battery power) technology that captures motions by detecting infrared radiation (radiant heat) emitted or reflected by objects. When the camera is mounted behind a window/glass, infrared radiation does not pass through the window/glass. As a result, the "Motion Detection feature" does not work reliably. If you want the camera to detect motions outside, it is recommended that you mount the camera outside.