A method of safeguarding the authorized access to field a device used in automation-technology, wherein the field device comprises an internet protocol capable interface as well as an interface for near field communication. The method comprises a unique factory installed access code for an authorized field device user is stored in the field device or clearly assigned to the field device; before delivery of the field device from a field device supplier to a field device user The unique factory installed access code for an authorized field device user is read from the field device through the near field communication interface means of a mobile service unit with the use of a Security App, made available by the field device supplier, or through an alternatively made available, and secure, channel of communication; access authorization for the field device is established by means of the Security App for at least one authorized field device user; and operation of the field device is accomplished by the authorized field device user with the established access authorization by means of the mobile service unit or the internet protocol capable interface.