Each access point (i.e. a door, a parking gate) generally has a human interface device (keypad, card and card reader, biometrics station, etc...). The function of the human interface device is to receive and authenticate access requests (i.e. determine who is requesting access and make sure they are who they claim to be).

Once the identity has been proclaimed valid by the human interface device, a Wiegand code identifying the requestor is sent to an access controller.

The controller's function is to authorize or deny access to the requestor (send a signal to lock or unlock the door, open or close the gate, etc...), based on a permission database (i.e. does the requestor have the right to access the area to which access is requested at this day and time). Many such controllers may also be networked together, thereby forming an access control network. Many of these networks may be connected to monitoring and control centrals which oversee the entire security system.

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