Localization of mobile phones brings opportunities for example in crime prevention or rescue operations. However, it also has the capacity to intrude the user's privacy, especially in conjunction with data retention (Vorratsdatenspeicherung). This work exploits the possibility to locate mobile phones based on their received signal strength of surrounding stations. It introduces a particular passive localization method. A detailed description about the theory and functionality is presented and an estimation of its accuracy is shown based on experiments. As the introduced localization is done...