If you use the Video Doorphone System to see who's at the front door before you open it, you can expand your system to check who is at the back door, as well, by adding this surface-mount camera. The Extra Surface-Mount Door Camera for Video Doorphone System will trigger the monitor that comes with the Video Doorphone System when your visitor rings the doorbell to your second entrance, allowing you to pick up the handset and talk. You can even let your guest inside by pressing the monitor's "open" button to unlock the door (electric door strike required for this feature and sold separately). A flush-mount camera is also available. # Camera # Wall bracket # Instructions