Abstract: A method is described of operating a radio system having a transmitter unit (10) and a receiver unit (11). At the transmitter unit, at least a potion (50) of an address is transmitted repeatedly for a predetermined period of time (T.sub.w), followed by a message. The receiver unit switches from a dormant, low power mode to a receive mode after a period of time in the dormant mode not exceeding the predetermined period of time (T.sub.w). In the receive mode address information is received and compared bit by bit with a predetermined address stored at the receiver unit. The receiver revels to the dormant mode as soon as a negative comparison is made, to a predetermined degree of non-correlation, between address information received and the predetermined address, thereby saving battery power.