To protect and watch transport units consisting of a towing unit and one or more transported or transporting units, the towing unit has a data processing system (1) capable of communicating with the outside world via communications and GPS satellites (45) and/or a GSM system (39) and with tags (10B) burried in a road. The transporting or transported unit or units additionally have a data processing system (15) capable of communicating with a data processing system (1) in the towing unit via a wireless interface (7) or interface (8). The data processing system in the transporting or transported unit or units is moreover interfaced with an aerial (16) capable of communicating with tags in a road or surfaces (10B) or tags (10A) located in the top of transporting or transported units. A system designed as described above provides the advantage that a cargo or a transport unit can always be positioned and watched.