D
Damper
A valve or plate regulating the flow of air or other fluid.
Data
Information, specifically in digital systems, that is operated on and produces an output, in contrast to commands or control signals.
Datagram
A packet of data unique to a specific protocol. Datagrams are placed within network frames for delivery over the network.
Data Service Unit (DSU)
A component of customer premises equipment used as an interface to a digital circuit. For example, DDS or T1. Combined with a Channel Service Unit (CSU), it converts a customer’s data stream to bipolar format for transmission.
Day Zone (DY)
A zone type that buzzes the keypad and provides a trouble report to the monitoring center if the zone is tripped while its area is disarmed and an alarm if the zone is tripped while the area is armed. This is typically used with window foil, emergency zones, or other types of protection that need constant supervision but not always an alarm. The keypad buzzer initiated by a day zone can be silenced by pressing any top row select key.
Dead Short
A short circuit having extremely low (or virtually no) resistance.
Dealer
An alarm company that leases or sells alarm systems.
Decibel (dB)
A measurement used to compare measured levels of sound energy (intensity) to the apparent level detected by the human ear, expressed as a logarithmic ratio.
Defer Test Time
A programming option that allows the panel to defer sending a scheduled Test Report if it has already communicated with the monitoring center receiver within the time period entered into the Test Frequency option. See Test Frequency.
Delay Reports
A programming option under Events Manager that allows all non-alarm reports to be held in panel memory until the event buffer is nearly full or until the next panel communication with the receiver.
Delay Zone
See Exit Zone.
Deluge Sprinkler System
A sprinkler system with open sprinklers where the water is controlled by a manually or automatically operated valve that allows heavy concentrations of water to deluge the area.
Derived Channel
A signaling line circuit that uses the public switched network local leg as an active multiplex channel while simultaneously allowing that leg to be used for normal telephone communications.
Detector
A device installed at a location in a security system that is designed to detect an intruder, rise of temperature, presence of smoke, etc.
Device
Any keypad, expander, or point addressable module that requires an address on the keypad or LX-Bus.
Device Fail Output
A programming option that allows the specified output to turn on any time an addressed device fails to respond to panel polling. The output turns off when all programmed devices respond to polling.
Dynamic Host Configuration Protocol (DHCP)
A protocol for assigning dynamic IP addresses to devices on a network. With dynamic addressing, a device can have a different IP address every time it connects to the network. In some systems, the device IP address can even change while connected.
DHCP also supports a mix of static and dynamic IP addresses. Dynamic addressing simplifies network administration because the software keeps track of IP addresses rather than requiring an administrator to manage the task. This means that a new computer can be added to a network without the hassle of manually assigning it a unique IP address. Many IPSs use dynamic IP addressing for dial-up users.
Digital Alarm Communicator Receiver (DACR)
A system component located in the supervising station that accepts and displays signals from the DACT sent over the public switched telephone system.
Digital Alarm Communicator System (DACS)
A system where signals are transmitted from a DACT located at the protected premises through the public switched telephone network to a DACR located at the supervising station.
Digital Alarm Communicator Transmitter (DACT)
A system component at the protected premises where initiating devices or groups of devices are connected. The DACT seizes the connected telephone line, dials a pre-selected number to connect to a DACT in the supervising station, and transmits signals indicating the initiating device status change.
Digital Dialer (DD)
Also known as Digital Communicator.
A programming option for the panel to use the DMP Serial 3 format for communication to the SCS-1/SCS-1R central station receiver.
A device that transmits alarm signals and other information to a central station using the existing customer phone line. To transmit an alarm, the communicator seizes the customer’s phone line and electronically dials the monitoring center’s receiver. When the receiver answers, the communicator sends a message in the form of a sequence of tones. A minicomputer in the receiver accepts and acknowledges the message, then prints out the information for display to the operator.
Digital Video Recorder (DVR)
Records analog security cameras that are connected via a coax cable. See Network Video Recorder (NVR). Both DVR and NVR record cameras and offer similar options but record different transmission methods.
Direct-Connect Alarm System
An alarm system connected to a police or fire department.
Direct Current (DC)
Electrical current that travels in only one direction and has negative and positive polarity. It may or may not have an AC ripple component. DC sources that are unfiltered should be referred to as full-wave or half-wave rectified AC.
Direct Wire
A dedicated leased telephone line from the subscriber premises that connects directly to a monitoring center.
Disarm
To turn off the burglary protection in an area using a keypad, keyswitch, or remote programmer.
Disarmed Rings
The number of rings the panel counts before answering the phone line when any system areas are disarmed.
Display Events
A User Menu option that allows authorized users to view a record of events that occurred on the system. The panel stores all alarms, troubles, restorals, and other options, in memory.
Door Access
A feature that allows a user to enter their code number and cause an internal Form C relay to activate and release an electric door strike or magnet. A door access report containing the keypad address and user number can also be sent to the monitoring center.
Door Prop
A programming option for XR Series Control Panels that sends an Open message to the keypads and a Zone Fault to a receiver when a door is left open past the specified amount of time.
Door Status Switch (DSS)
A switch used to monitor whether a door is in an opened or closed position.
Double Pole, Double Throw (DPDT)
A switch or relay output contact (form C) that has two separate switches operating simultaneously, each with a normally open and normally closed contact and a common connection. This form is used to make and break two separate circuits.
Dry Contacts
Generally, relay contacts that are isolated from the circuit board and power supply and have no voltage applied to them. They can be opened, close, or a combination of both. See Form “A” Contacts, Form “B” Contacts, and Form “C” Contacts.
Dry-Pipe Automatic Sprinkler System
An automatic sprinkler system where piping from the alarm check valve to each sprinkler head contains air under pressure. This pressure holds the alarm valve closed, keeping water out of the system. This type of system is used where there is danger of water freezing if it remains in the system piping.
Dual Reporting
A method of sending the same signals to two separate receivers. For example, sending alarms and openings/closings to receiver 1 and receiver 2.
Dual-Tone Multiple-Frequency (DTMF)
A feature that enables touch-tone dialing.
Duct
A passageway made of sheet metal or other suitable material, not necessarily leak-tight, that is used for conveying air or other gas at low pressures.
Duct Type Smoke Detector
A device located within a duct, protruding into a duct or located outside a duct that detects visible or invisible particles of combustion flowing within the duct. Actuation of the device may allow operation of certain control functions.
Duplex
Simultaneous, independent, two-way data transmission.
Duress
See Ambush and Ambush Code.
Dynamic Address
Generally refers to a computer location address that is variable. The opposite of dynamic is static.