When someone needs a video intercom at their doors, the Expandable Recording Color Video Intercom System 
at IntercomsOnline.com is the unit we like to recommend. Not only does this unit send live audio and video to the indoor 4-inch, full-color monitor when someone rings the doorbell, it also records full motion video and audio on to a Secure Digital (SD) card that you can place in your computer to copy and view it. If someone breaks in to your home or business, most likely they’ll ring the doorbell to make sure no one is there (and pretend they’re selling something if you are). Since the Expandable will make record this event you’ll have a nice video to show the police.
Not only this system record, but as its name says it is expandable to a total of 2 cameras and 4 monitors. So you can handle both your front and back doors, plus put monitors throughout your house or business.
A built-in infrared system for night vision provides supplemental lighting to enhance night viewing. The door phone camera operates in color during daylight and black & white in low lighting conditions.
The 2-wire installation is easy and you can even add an external electric door lock to open the door from the indoor monitor and the door status indicator tells you when the lock is open!