An electricity meter comprising: · a housing including at least one housing element that is normally closed in operation, but that is capable of being opened; · a supercapacitor (C1); · a power supply circuit arranged to act, whenever the electricity meter is put into connection with electric power, to charge the supercapacitor; · a charge-maintaining circuit arranged, to act whenever the electricity meter is taken out of connection with electric power after previously being in connection with electric power, to prevent the supercapacitor from discharging so long as the housing element remains closed; · a discharge circuit arranged to act, whenever said electricity meter has been taken out of connection with electric power, to discharge the supercapacitor in the event that the housing element is opened; and · a processor circuit arranged to act, whenever the electricity meter is put back into connection with electric power after being taken out of connection with electric power, to acquire a detection signal representative of the voltage across the terminals of the supercapacitor and thus representative of the level of charge of the supercapacitor, and if the supercapacitor is discharged, to detect that the housing element has been opened since the electricity meter was taken out of connection with electric power; characterized in that the charge-maintaining circuit comprising two first transistors (Q1, Q2) and a second transistor (Q3), the two first transistors being connected back-to-back, one of the first transistors (Q1) having a terminal connected to a terminal of the supercapacitor and the other first transistor (Q2) having a terminal connected to an input of the processor circuit, the second transistor being arranged to put the first transistors into a conductive state when the electricity meter is electrically powered and the supercapacitor (C1) is charged. · a housing including at least one housing element that is normally closed in operation, but that is capable of being opened; · a supercapacitor (C1); · a power supply circuit arranged to act, whenever the electricity meter is put into connection with electric power, to charge the supercapacitor; · a charge-maintaining circuit arranged, to act whenever the electricity meter is taken out of connection with electric power after previously being in connection with electric power, to prevent the supercapacitor from discharging so long as the housing element remains closed; · a discharge circuit arranged to act, whenever said electricity meter has been taken out of connection with electric power, to discharge the supercapacitor in the event that the housing element is opened; and · a processor circuit arranged to act, whenever the electricity meter is put back into connection with electric power after being taken out of connection with electric power, to acquire a detection signal representative of the voltage across the terminals of the supercapacitor and thus representative of the level of charge of the supercapacitor, and if the supercapacitor is discharged, to detect that the housing element has been opened since the electricity meter was taken out of connection with electric power; <EOS>