Thrifty mains-slave unit

A mains-slave unit has a master outlet and one or more slave outlets. The master outlet is connected permanently to the mains, but the slave outlets via a relay (or similar switching element). When the equipment connected to the master Durlet is switched on, the mains-slave unit detects that a current flows througb the rransformer and arranges for the slave outlers to be connected to the mains as well.