Abstract: A method and a detector for controlling coins inserted into a slot of a device are disclosed, in which a device for imparting oscillations to a coin is arranged, The frequency of oscillations is measured and compared with a predetermined value in an electronic device which actuates a coin separating device which guides unsuitable coins into a separation passage.

Abstract: A plurality of selling machines is provided with coding devices assigned to each machine and connected via a telephone network to a central switching station and via subscriber lines to individual subscriber stations. Each machine is provided with sensors of predetermined operational conditions and/or interferences in the machine, the sensors delivering an output signal which is connected to the coding device. In the coding device the signal is coded according to the particular operational condition and/or interference and combined with a primary recognition signal. The combined coded signal is transmitted to the switching station where the recognition signal is identified and the remaining signal is switched over and transmitted to the subscriber station. In the subscriber station, the signal is processed in a computer and the output message is displayed on a display board and recorded in a printer.