The KH I sometimes attend has had cameras for awhile. There is a monitor in the lobby that the attendants use to monitor the front door (doors are locked about 15 min after the meetings start) and the parking lot. Anyone can see the feed, it's actually on a wall in clear site. Seems to make sense for security purposes to me. It's better than having some poor attendant patrol the parking lot.
I've also seen one inside at a double auditorium KH where they can hold a larger meeting and broadcast to both auditoriums at once. And at AH's they have them.
Some of the comments are insane.