A system is described, for monitoring at least a household electric user (HA1-HA4), in particular a household appliance, where a monitoring device (MSA) is connected between a source of electric energy (OUT) and said user, said monitoring device (MSA) comprising metering means for detecting one or more electric quantities being associated with the operation of said user (HA1-HA4). According to the invention, said monitoring device (MSA) comprises - control means programmed for - comparing the electric quantity or quantities being measured through said metering means with reference values of said electric quantity or quantities which are stored within said control means; - generating, in function of said comparision, information being representative of the current status or phase of operation of said electric user (HA1-HA4); - allowing for the reading or transmission of said information to the outside of said device (MSA); - communication means, for realizing a transmission and/or reception of data or information on the electric supply line which connects said user (HA1-HA4) to said device (MSA), by means of a modulation of electric power between said user (HA1-HA4) and said device (MSA) and/or vice-versa.