A fastening device of a penis extension device includes a coupling element for exerting a tensile force on a penis and a tensile force meter, a first electronics component and a first current source. The tensile force meter electrically or electronically determines the measurement value for the exerted tension together with the first electronics component, and the first electronics component has a first radio device for transmitting the determined measurement value to an external receiver. With this device it is possible for a relevant measurement value, in particular the measurement value for the exerted tensile force, to be transmitted from the sensitive area in which the fastening device is used to an external device, for example to an app of a cell phone.
