Decibel
a relative measure of the difference between the power level of two signals. The signal strength of a door/window sensor in a residential system might range from .1mW for a close-in transmitter to .00000000001mW for a transmitter in a remote closet.

Delay
the time allotted the system user to exit the premises after turning the system on without causing an alarm (exit delay); the time allotted the system user to enter the premises and turn off the system without causes a false alarm (entry delay).

Disarm
to turn the system or a sensor off.

Diversity
to eliminate the effects of multipath distortion, diversity communications systems use redundant signal paths between the transmitter and receiver.

Door/Window Sensor
a device for detecting the opening of a door or window and for sending a signal to the control panel indicating the change of state.

DVMR
Digital Video Multplexer/Recorder. A device that receives images from several CCTV cameras at once and enables the images to be viewed on a monitor or recorded.