Abstract: A process is disclosed for protecting watercraft against theft in an area delimited in space, for example a harbor, using a stationary transmitting/receiving unit and an on-board transmitting/receiving unit. When interrogated by the stationary unit, the on-board unit emits a characteristic identification signal. The identification signal contains a basic key that identifies the watercraft and the identification signals of all watercraft in the harbor are stored in a central computer. To legitimize use of the watercraft, a legitimization key is input into a central computer before departure. The central computer ascertains whether the use of the watercraft is legitimate based on the interrogation carried out by the stationary transmitting/receiving unit and, if required, triggers an alarm and information program.