Method for the safeguarded operation of a safety-critical device by means of a mobile communication terminal, wherein - a user-side operating command is detected by the mobile communication terminal, wherein two data processing processes which are independent of one another are used for data retention and data processing, one of which is active and causes the detected operating command to be displayed on the screen of the communication terminal, and the other of which initially runs in parallel, - operating information relating to the detected operating command is transmitted from the mobile communication terminal to the safety-critical device, wherein the detected operating command is processed by both data processing processes and the operating information formed in each case is transmitted separately to the safety-critical device, - acknowledgement information is generated by the safety-critical device in a form which is extraneous to the communication terminal and cannot be generated by either of the data processing processes and is transmitted to the mobile communication terminal, wherein the safety-critical device checks the received operating information for conformity and plausibility and if the result of the check is positive generates the acknowledgement information, - based on the transmitted acknowledgement information, activation code information is generated by the mobile communication terminal in a non-machine-evaluable form and is displayed together with the acknowledgement information on the mobile communication terminal, - an acknowledgement response formed by a combination of the activation code information with a user-specific operation is detected by the mobile communication terminal and is transmitted by the mobile communication terminal to the safety-critical device together with a hash value formed from the acknowledgement information, and - if the check on the acknowledgement response and the hash value is successful, the operation of the safety-critical device is executed. - a user-side operating command is detected by the mobile communication terminal, wherein two data processing processes which are independent of one another are used for data retention and data processing, one of which is active and causes the detected operating command to be displayed on the screen of the communication terminal, and the other of which initially runs in parallel, - operating information relating to the detected operating command is transmitted from the mobile communication terminal to the safety-critical device, wherein the detected operating command is processed by both data processing processes and the operating information formed in each case is transmitted separately to the safety-critical device, - acknowledgement information is generated by the safety-critical device in a form which is extraneous to the communication terminal and cannot be generated by either of the data processing processes and is transmitted to the mobile communication terminal, wherein the safety-critical device checks the received operating information for conformity and plausibility and if the result of the check is positive generates the acknowledgement information, - based on the transmitted acknowledgement information, activation code information is generated by the mobile communication terminal in a non-machine-evaluable form and is displayed together with the acknowledgement information on the mobile communication terminal, - an acknowledgement response formed by a combination of the activation code information with a user-specific operation is detected by the mobile communication terminal and is transmitted by the mobile communication terminal to the safety-critical device together with a hash value formed from the acknowledgement information, and - if the check on the acknowledgement response and the hash value is successful, the operation of the safety-critical device is executed.