A method of determining a state of access control devices and sales or payment machines of an access control system, wherein the sound profile in the audible or an ultrasonic range emitted during operation by a component or a component group of an access control device or a sales or payment machine of an access control system is detected, permanently or in predetermined time intervals, by at least one microphone and on the basis of the recorded sound profile, an acoustic identification signature is created in a server or a central computer, which identification signature is based on the frequency spectrum of the recorded sound profile and/or the time variation thereof, wherein the acoustic identification signature is assigned to a component or a component group and compared with an acoustic reference identification signature which is stored in the server and assigned to this component or component group, characterized in that in the event of detection of a deviation of the detected acoustic identification signature from the acoustic reference identification signature stored in the server, which deviation exceeds a predetermined first threshold value, an increased wear of the component or the component group is detected, and if the deviation of the detected acoustic identification signature from the acoustic reference identification signature stored in the server exceeds a second threshold value, which is higher than the first threshold value, a defect of the component or the component group is identified, wherein, in a context of a learning phase, usual sounds during operation of an intact access control device or an intact sales or payment machine of an access control system are recorded by the at least one microphone, wherein the recorded sound signals are, in each case, assigned to one component or one component group, and wherein acoustic reference identification signatures for the components or component groups are created from the recorded sound signals and stored in the server, wherein the assignment of the recorded sound signals and thus the reference identification signatures to the components or component groups takes place whereby the beginning of the operation of the access control device or the sales or the payment machine is detected on the basis of the signals delivered by at least one microphone, wherein, taking account the known precise sequence of the individual operations of the access control device or a sales or payment machine, the sound signals are, in each case, assigned uniquely to one operation and thus one component or one component group or whereby the access control devices and sales or payment machines of the access control system are connected to the server for the purpose of data communication and the information as to which component or component group is active is transmitted to the server in real time so that the recorded sound signals are assigned, in the server, to the currently active component or component group in each case, wherein a detected identification signature is assigned to a component or component group on the basis of characteristic properties of the sound profile emitted by the component or component group or wherein a detected identification signature is assigned to a component or component group whereby on the basis of a known precise sequence of the individual operations during the operation of an access control device or the sales or payment machine of the access control system, the detected identification signature is uniquely assigned to one operation and therefore one component or one component group, wherein the start of operation of the access control device or the sales or payment machine is identified on a basis of the signals delivered by the at least one microphone or wherein the access control devices and sales or payment machines are connected to the server for data communication, and the information as to which component or component group is active is transmitted to the server in real time so that the assignment of a detected identification signature to a component or component group takes place in this manner.