Abstract: A conventional electric utility meter is equipped with special circuitry and components which work in conjunction with an inserted magnetic card to regulate the supply of electricity to the structure to which the unit is attached. In addition to including the conventional dials which indicate overall kilowatt hours, the exterior of the unit includes a receptacle for the card and additional displays which show the kilowatt hours, and corresponding dollar value thereof, for the current payment period. The special circuitry includes a microprocessor, a set of magnetic read/write/erase heads, and a power relay. The circuitry interfaces with the conventional meter components by means of a photocell positioned above apertures or notches in the rotating disk of the meter. In the primary mode of operation, a prepayment card is inserted containing a predetermined kilowatt hour credit. The special circuitry senses this amount and adds it to the amount of power the customer is entitled to receive.