Abstract: A display device has a time-constant circuit and a switching element such as a transistor for supplying the voltage of a battery to the time-constant circuit when a battery check key is pressed. A microcomputer measures a time interval from a time when the voltage of the battery starts being supplied to the time-constant circuit to a time when a voltage of the time-constant circuit reaches a predetermined value, and determines the remaining electric energy of the battery from the measured time interval. The microcomputer supplies data to a display unit which then displays a progressively variable display mark combination representative of the determined remaining electric energy of the battery.

Abstract: A cordless telephone utilizes internally generated identifying codes to reduce crosstalk and the risk of wiretapping. When the handset unit is mounted on the base unit, a new identifying code is automatically generated and stored in the base unit, and then transmitted to the handset unit, which also stores it. When an incoming or outgoing telephone call is initiated, the two identifying codes stored in the base unit and the handset, respectively, are compared and, if they are not identical, the telephone call is cut off. Advantageously the identifying codes are randomly generated.