A normal security provision in a data centre and trading floor is some form of CCTV monitoring and recording of key areas within and around the organisation's building. A visit to IFSEC at the National Exhibition Centre in Birmingham UK will quickly convince you there are thousands of different CCTV security solutions. The art of placing the cameras is a balance between risk/cost. The costs involve installation, power, cabling, capital cost for equipment, operational cost for use and long term image storage. The more cameras you have the greater the capital cost and the greater the operational cost.
These systems can have great deterrence effect and can help in the detection of offenders intent on crime. However if the cameras are poor quality and not well placed they can be a waste of money. If the criminals are aware of the camera locations they can avoid their faces being recorded. Simple techniques such as looking away and "hoodie" type clothing can destroy the effectiveness of the CCTV systems. The careful positioning of some hidden or covert cameras as part of the overall security system can help to detect the faces of criminals who would otherwise attempt to defeat the visible or overt cameras. Hidden cameras can be positioned at eye level to record facial images whereas overt cameras may have to be positioned at a high level to prevent damage by criminals.
I'll relate a true life example which happened in a major international bank. The bank in question had a good CCTV security system protecting access to its data centres. The visible camera systems were of high quality, were well positioned, and the CCTV recording system provided good quality playback. One of the Bank's data centres was subjected to a raid by well organised thieves during the evening after the day time computer operators had left. The entrance to the building was protected by 24 hour security guards. A thief "tailgated" one of the operations staff during the day to gain access to the main technology area and hid somewhere in the room. This was a suspected, but never proved "inside job". Later in the evening the hidden man opened the door to the data centre to allow access to other thieves who were disguised as cleaners. They wheeled in a large high sided trolley into the technology area and set to work pulling Sun servers from the computer racks/cabinets and loading them into the trolley. It was a crude process as they were pulling live operational servers from the cabinet without first powering down the machines. In less than five minutes they'd filled the trolley with expensive Sun servers. They covered the trolley and wheeled it out of the building under the watchful(!) gaze of the security guard who assumed they were departing cleaners. The stolen equipment value was in excess of £200,000 but the greater cost was the recovery of the systems the following day.