Security system.

摘要

Electrical appliances (1) each include a module which carries a code. Whenever mains electrical power is reconnected to an apparatus (1), FSK signals are sent via the electricity main circuit (11) to a security module (10). The security module (10) causes a call to be set up via a telephone network (represented by line (7) Interface (8) and switch (9)) to a security unit (12). The security unit (12) uses customer line identity (CLI) signals from the interface (8) to identify a code which it returns via the network to the security module (10). The module (10) forwards the received code using FSK signals to the requesting apparatus (1) by way of mains circuit (11). If an incorrect code (or no code) is received the module in the apparatus (1) inhibits the supply of power to operational circuits.