There was another post regarding door phones with a camera in it. Normally these units have some sort of an interface box that connects up to your TV monitor with a composite video output connector (RCA). The problem with this is, if you are watching another source (like cable), when the doorbell rings, you have to switch your TV source to another input to see the camera.

I was told there was a unit available with a "loop through" capable of allowing your existing source to be watched and the camera would automatically inject the signal when the door bell rang (or a motion detector triggered). I would think it can only work with external sources so you would have to have a digital cable box or satellite receiver.

Has anyone seen something like this? I tried googling, but I'm not sure what to call it.