ASDE-X is an automated system that alerts tower and ground controllers to collision hazards on the airport surface. A transponder is a device that either responds to radar pings or continuously broadcasts the vehicle's position. They are mandatory equipment for aircraft, and at most large airports they're required for all ground vehicles too. The two systems work together.
If the truck had had a transponder, ASDE-X would've automatically alerted the controller who was working that night. So there's another link in the chain, in addition to the staffing issue and the failure to visually clear the runway.
