1. A selective call radiotelephony system having a central radio transmitting and receiving station and a plurality of mobile radio transmitting and receiving stations located within radio range of the central station, each radio transmitting and receiving station having an associated selective call or identification, the selective calls containing different criteria or addresses for performing different functions, characterized in that normal radio telephone traffic from the central station or from the mobile stations is initiated by selective calls (1) or identifications having a first criterion common to all the radio subscribers, and that calls (6) in the form of selective calls, which have a second criterion common to all the portable stations, are transmitted successively and cyclically repetitively from the central station to the individual mobile stations for the purpose of monitoring the persons operating the mobile stations, that each call identified by a mobile station is acknowledged by an acknowledgment call (= identification) which is initiated within a predetermined period of time by the person operating the relevant mobile station and is transmitted to the central station, and that, in the event of an anticipated acknowledgment call failing to arrive, an optical and/or acoustic alarm signal identifying the relevant mobile station is automatically triggered in the central station after the predetermined period of time has expired.
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