As the X-10 protocol is patented any non X-10 devices wishing to transmit or receive commands (like a PC or HA controller) must use an interface like the TW523.
This is an adapted American unit so it comes with as USA style 2-pin plug . The unit is capable of transmitting and receiving X-10 commands. It is attached to the PC. HomeVision (or whatever) by a 4-wire cable (RJ11 socket on the unit). A signal activity LED shows when the unit is transmitting X-10 commands.
Seems to have been replaced by the “CE Approved” TW7223 (although I have no experience of this module).