If the transmission of the data doesn’t work due to the distance between sending unit and GSM-box, then a repeater has to be interconnected. The repeater receives the signals of the sending units, amplifies and transfers them to the GSM-box. If necessary, several repeaters (any number) can be connected in series. The needed socket for the repeater can be continued to use, as it has a built-in socket. Outdoor repeaters are available in protection class IP67. Please find the technical details under https://www.frowein808.de/products/PERMANENT-MONITORING/.