Security cameras can be viewed from most modern BeoVisions - they will all have Composite inputs which are activated by adding "CAMERA" to the Beo4 remote controller.
Many like this setup - if the doorbell rings they can immediately switch onto the CAMERA channel and see who's there! Those with PiP functionality can ever watch normal television with a tiny box in the top corner of their picture showing the exterior view - very handy!
The easiest way I've seen this done, though, was through a security camera linked to the home's RF (Co-Ax) aerial system - it simply came through like any other TV channel.
Simple to setup as well (apparently) - just run a cable out from the camera's master unit, and into the splitter for the home!