Data acquisition system for acquiring vehicle data of a vehicle, comprising: a first data acquisition unit; a second data acquisition unit connected via a data link to the first data acquisition unit in order to thus transmit vehicle data from the first data acquisition unit to the second data acquisition unit; an attachment mechanism designed to attach the second data acquisition unit to the vehicle in an attached state; a release mechanism designed to release the attachment of the second data acquisition unit to the vehicle and thus to move the second data acquisition unit to a released state in which the second data acquisition unit is physically separate from the vehicle; wherein the release mechanism is further designed to release the attachment of the second data acquisition unit to the vehicle based on a forecast for a vehicle state of the vehicle; wherein the second data acquisition unit is designed to maintain the data link for transmitting the vehicle data between the first data acquisition unit and the second data acquisition unit in the released state by means of a radio link, characterized in that the second data acquisition unit is designed to maintain the data link for at least as long as until the second data acquisition unit receives from the first data acquisition unit a termination signal which has been transmitted at the time when the first data acquisition unit is no longer able to record information about voices or sounds on board the vehicle or vehicle data; wherein the first data acquisition unit is designed so that it transmits the termination signal when the first data acquisition unit can no longer record information about voices or sounds on board the vehicle or vehicle data; and wherein the termination signal can be used to detect and verify that a data set of the second data acquisition unit fully corresponds to a data set of the first data acquisition unit and that all data recorded by the first data acquisition unit are also recorded and stored by the second data acquisition unit. a first data acquisition unit; a second data acquisition unit connected via a data link to the first data acquisition unit in order to thus transmit vehicle data from the first data acquisition unit to the second data acquisition unit; an attachment mechanism designed to attach the second data acquisition unit to the vehicle in an attached state; a release mechanism designed to release the attachment of the second data acquisition unit to the vehicle and thus to move the second data acquisition unit to a released state in which the second data acquisition unit is physically separate from the vehicle; wherein the release mechanism is further designed to release the attachment of the second data acquisition unit to the vehicle based on a forecast for a vehicle state of the vehicle; wherein the second data acquisition unit is designed to maintain the data link for transmitting the vehicle data between the first data acquisition unit and the second data acquisition unit in the released state by means of a radio link, characterized in that the second data acquisition unit is designed to maintain the data link for at least as long as until the second data acquisition unit receives from the first data acquisition unit a termination signal which has been transmitted at the time when the first data acquisition unit is no longer able to record information about voices or sounds on board the vehicle or vehicle data; wherein the first data acquisition unit is designed so that it transmits the termination signal when the first data acquisition unit can no longer record information about voices or sounds on board the vehicle or vehicle data; and wherein the termination signal can be used to detect and verify that a data set of the second data acquisition unit fully corresponds to a data set of the first data acquisition unit and that all data recorded by the first data acquisition unit are also recorded and stored by the second data acquisition unit.