Once entrances to a facility are limited in number, the process of allowing or denying access is generally accomplished through one of four approaches. The first and most common approach is manpower intensive, and the remaining three employ technology devices. The level of actual security achieved is generally believed to be from 1 to 4, lowest security to highest security, but this is subject to many other variables. These four approaches are:

1. A security guard controls entry; ID cards or other means of identification may be checked. (WHO lets you in)
   
2. A special ID card/badge with automatic readers. (What you HAVE)
   
3. A PIN number for entering on a keypad. (What you KNOW)
   
4. A biometric device for feature recognition. (Who you ARE)

The following sections provide further details. The second, third, and fourth approaches utilize technology, as illustrated in exhibit 4.2.