Most Digital Video Recorders have 4, 8, 16 and 32 camera inputs. If you own a 4 camera DVR and want to add a 5th camera you would need to upgrade to an 8 camera unit. Recently we received a call from one of our customers who owns an apartment building in Beverly Hills. She had an 8 channel DVR with 5 cameras already installed. She was having a problem with cars being vandalized and thought that the perpetrators were following the tenants through the parking gate as they entered the property. Once we played back the video from the driveway gate camera we saw she was correct. We added an infrared license plate camera to log all of the cars entering the property. So once we had the license plate logged, and than viewed the other wide angle infrared bullet cameras we had concrete proof to give to the police. But the real moral of the story is, sometimes its better to buy a DVR with a larger camera capability for the future. It will save you money in the long run. If you have an apartment building in Beverly Hills, Santa Monica, Culver City, The Wilshire District, Marina Del Rey or Venice or even Manhatten, Hermosa or Redondo Beach, call for a quote to upgrade your existing system.