Physical security

Physical security describes measures that prevent or deter attackers from accessing a facility, resource, or information stored on physical media.

Physical security can be anything from a locked door to multiple layers of armed guardposts.

The field of security engineering has identified three elements to physical security:

obstacles, to frustrate trivial attackers and delay serious ones
alarms, to make it likely that attacks will be noticed
security response, to repel, catch or frustrate attackers when an attack is detected

The main intent of physical security is to deter attackers by persuading them that the likely costs of attack exceed the value of making the attack.

For example, ATMs (cash dispensers) are protected, not by making them invulnerable, but by spoiling the money inside when they are attacked. Attackers quickly learned that it was futile to steal or break into an ATM if all they got was worthless money covered in dye.

Hiding the resources, or hiding the fact that resources are valuable, is good too -- cite diamond dealers doing business by mail.