Abstract: The circuit arrangement in a communication system which is protected by subscriber-specific passwords having a memory which contains all the possible passwords and a comparator which compares each received password with the memory content. A monostable delay circuit with a subsequent logic combining gate, are connected to the output of the comparator (2) via an input gate (5). The monostable delay circuit and the logic combining gate are such that in the presence of an energizing signal applied to a special input (C), when there is non-agreement between the received and the stored passwords the monostable delay circuit starts and during operation inhibits the logic combining gate, while when there is agreement the logic output gate (6) is enabled. Such a circuit arrangement can be provided before each selector stage of a switching system of before each accessible channel of a mobile radio system.