A lock refers to a number of types of device for securing a door. While there are combination locks, smart card locks, and keyed locks, the mechanism known as a cipher lock is opened with a programmable keypad and — according to definition — is not a true lock. There is also a specific type of cipher lock called a Cypher Lock®, which was developed by Continental Instruments, now a division of Napco Security Group.
The U.S. Army distinguishes the use of cipher locks and keyed locks, stating that the purpose of keyed locks is to maintain physical security, while the purpose of cipher locks is to control access, limiting either unannounced intrusions or unescorted entry to particular areas of a facility that are sensitive. Cipher locks are used to control access to areas such as airport control towers, computer rooms, corporate offices, embassies, areas within financial institutions, research and development laboratories, and storage areas holding weapons, controlled substances, etc.
A cipher lock may have four or five pushbuttons, depending on the manufacturer. Even with five pushbuttons, the code may be one to five digits. When the cipher lock unit is set up the code is programmed and shared with authorized personnel. It can be changed at any time.
Cipher locks are available in a variety of metallic colors and can be equipped with either a knob or a lever. The system may be mechanical, as is the case with the cipher locks made by Simplex or electronic, as is the Cypher Lock®. An electronic system allows for unlocking the door from a location within the room when a visitor who does not have the code arrives.
The Cypher Lock® in particular can be combined with a set time for opening the door as well as a battery standby system. Three types of alarm system are available. A burglar alarm interface is available to indicate when the door is breached. An error alarm can reveal someone who tries to guess the code. Finally, a hostage alarm can be triggered to indicate that entry was made under duress.