This DataLine Surge Protector protect your RJ11 port against power surges. It provides protection on all 4 lines and perfect for RS232 serial and other communication devices including short-haul modems, concentrators, switches and repeaters. It has extremely sensitive, state of the art avalanche-diode technology. It has high speed throughput, automatic reset after surge, rugged & stylish with easy In-Line installation and negligible signal loss. (Connectors: RJ11 Male to Female; Surge Capacity: 18.0v)