Electronically Coded Devices

Electronically coded devices include electronic and computer-controlled keypads. The common telephone keypad (12 keys) is an example of an electronic keypad. This type of keypad consists of simple push-button switches that are decoded by digital logic circuits. When the correct sequence of buttons is pushed on a keypad used to control entry, an electric signal unlocks a door for a few seconds. The correct sequence of buttons can be figured out by unauthorized persons who can view the keypads while they are being used or who can examine the keys closely. Viewing and access to the keypad must be restricted.

A computer-controlled keypad is similar to other keypads, except that the computer-controlled keypad has a microprocessor in the keypad or in a separate enclosure at a different location. The microprocessor monitors the sequence in which the keys are depressed and may provide additional functions such as personal identification and digit scrambling. When the correct code is entered and all conditions are satisfied, an electric signal unlocks the door. Some of these keypads are designed with displays that can be seen only straight on and from very close, making it more difficult for an observer to figure out the correct sequence of keys.