Data vaulting
The process of sending data off site, where it can be protected from hardware failures, theft, and other threats. Several companies now offer Web backup services that compress, encrypt, and periodically transmit a customer's data to a remote vault. In most cases, the vaults have auxiliary power supplies, powerful computers, and manned security. Also referred to as a remote backup service (RBS).

Dead Bolt
A lock component having an end which protrudes form or is withdrawn into, the lock front by action of the lock mechanism. When the door is closed and the dead bolt thrown, it extends into a hold provided in the strike, locking the door and will not retract with end pressure.

Default
Preset values in the software which the System will use if the user does not change them.

Device Address
Value set on an access control device to determine its unique identity

Digital Signal Processing (DSP)
Digital signal processing (DSP) refers to various techniques for improving the accuracy and reliability of digital communications. DSP works by clarifying, or standardizing, the levels or states of a digital signal. A DSP circuit is able to differentiate between human-made signals, which are orderly, and noise which is inherently chaotic. In security, DSP is deployed in signaling devices such as motion detectors to minimize false alarms, and surveillance cameras to improve image quality.  

Digital Video Recorder (DVR)
Digital Video Recorder is the industry standard term applied to standalone and PC-based systems that record video images to a computer hard drive providing high quality recording. DVR’s provide a quicker method of retrieving the recorded information unlike media such as VHS tapes and other equipment that stores information in a sequential manner.  

Digital certificate
In the PKI environment, the data, equivalent to an identity card, issued to a user by a CA (Certificate authority), which he/she uses during business transactions to prove his/her identity.

Digital signature
The number derived by performing cryptographic operations on the text to be signed. This operation, or hash function (also called hash algorithm), is performed on the binary code of the text. The result is known as the message digest, and always has a fixed length. A signature algorithm is applied to the message digest, resulting in the digital signature.

Disabled
Turned off. Not active.

Disarm
The act of disabling or shunting a security system or portions of the system to ignore input signals that normally result in alarms. Disarming can occur with user intervention, such as pass codes entered into a keypad, or on schedule through a PC based Access Control System.  

Door Ajar
A condition that occurs when a door is left open after a valid user has passed through.

Door Contact
Contact switch activated whenever a door is opened. This switch monitors the door status (open or closed).

Door Control Relay
The relay used to control the unlocking and locking functions of door hardware in an access control system.  

Door Controller
A microprocessor based unit from which a number of doors may be controlled. The door controller makes the decision as to whether access is to be allowed.

Door Forced
A door forced alarm is the resulting logical alarm that occurs at a portal when the door is sensed to be in an open state without an associated valid access card transaction or an associated REX signal.

Door Open Time
The time allowed for a controlled door to remain open after a valid entry. At the expiration of this time, the system records a transaction which may be defined as an alarm. If the alarm bypass relay is used, it would also de-energize at the end of this time.

DSA
Digital Signature Algorithm. Presented in 1991 by the NIST and patented in 1993. A publicly available one-way algorithm used to generate or verify digital signatures of a text to be signed (not to encrypt/decrypt information). As input, DSA needs

1. The message digest of the message to be signed
2. The signer's private key
3. A random number

Its output is a pair of numbers (often referred to as r and s) which together, make up the digital signature.To verify a digital signature, DSA needs as input

1. The message digest of the text to be verified
2. The signer's public key
3. The value s from the signature

DSA then makes a computation, the output of which is called v, for example. If v = r, then the signature verifies.

DSS
Digital Signature Standard. Developed by FIPS (U.S. Federal Information Processing Standard). Adopted the DSA in the early 1990s.

Dual Control (2-men control)
Dual control is a security procedure that requires two or more people (or two or more devices) to cooperate in order to gain access to a restricted area.

Dual Technology
Utilization of two different technologies in one device to increase reliability and functionality. Dual technology motion sensors, for example, use both passive infrared and microwave technology in order to reduce false alarms and increase detection.  

Duress
A device, such as a push button or pull station, connected to a security system to signal an alarm when an individual is threatened or forced to do something. Bank Clerks typically have a duress alarm installed beneath their counter to signal robbery attempts.
Type of alarm activated by entering a special security code that indicates to the monitoring station that you have been "forced" to disarm your system.