Physical security is based on keeping intruders out. Out of the facility, out of the network and its wiring and wireless links, out of the computers, and out of the data stores. Much of physical security can be attained by common sense precautions, similar to keeping the cash safe in a business. Other measures are more obscure, such as adhering to the standards in data cabling and facility construction, such as providing adequate telecommunications pathways and spaces, and properly securing telecommunications rooms.
An important part of physical security is making sure that the people who must enter a facility are actually who they say they are. Proper identification procedures can include requiring badges and card readers at critical points, or actually measuring some attribute of the person, such as physical weight, appearance, fingerprints, or retina patterns. This kind of biometric security is increasing in its importance, and is appearing in more facilities all the time.