⇒ driver vigilance device(A dead-man's vigilance device (also called the Driver Vigilance Device or DVD for short) is a railroad safety device that operates in the case of incapacitation of the engineer. It is a hybrid between a dead-man's switch and a vigilance control. wikipedia.org)
DVD(A form of storage characterized by high capacity (roughly 650 MB) and the use of laser optics rather than magnetic means for reading data. Optical disk storage commonly used for audio, video, and computer data. DVDs range in capacity from 4.7 GB to 17 GB, and can store significantly more than a CD-ROM)
