An electricity meter includes a housing including at least one housing element that is normally closed; a supercapacitor and a power supply circuit arranged to act, whenever the electricity meter is put into connection with electric power, to charge the supercapacitor; both a charge-maintaining circuit arranged to act, whenever the meter has been taken out of connection with electric power, to prevent the supercapacitor from discharging so long as the housing element remains closed, and also a discharge circuit arranged to discharge the supercapacitor in the event that the housing element is opened; a processor circuit arranged to act, after the meter is put back into connection with electric power and in the event that the supercapacitor is discharged, to detect that the housing element has been opened since the meter was taken out of connection with electric power.