The invention relates to a method for operating a drive device (1) of a vehicle, in particular, a motor vehicle, said device having at least one electric or hydraulic machine (2) as a drive unit. Said method consists of the following steps: determining a target drive direction (ZR) that can be set by the driver of the vehicle, detecting a current direction of travel of the vehicle and comparing the current drive direction with the target drive direction (ZR) that has been set, detecting the direction of action of a current drive force and comparing the direction of action with the target drive direction (ZR), if the current direction of travel deviates from the target drive direction (ZR), detecting/determining unauthorised driving of the vehicle, if the direction of action deviates from the target drive direction (ZR). The invention also relates to a device and a system, in particular, for performing the method.