Communications and alarm system to connect temporarily, at short distance, portable radio transceivers with an entry door intercom installation

摘要

Communications and alarm system among people that are, respectively, outside and inside a building equipped with an entry door intercom installation including one external calling station located on the side of the building's entry door and several answering stations located inside the apartments and linked to the calling station, on one hand, by means of a bidirectional talking channel common to all stations and, on the other hand, by means of separated unidirectional calling channels. According to the invention, one radio transceiving and switching set is provided, connected to said calling station, by means of which, transmissions are possible from and to a plurality of portable radio transceivers, all tuned on the same frequency, being each of them enabled to transmit at least a coded calling radio signal peculiar to the transceiver. Said transceiving and switching set is enabled to recognize, on the basis of said signal's decoding, only one pre-set answering station of the entry door intercom installation, in order to establish a communication link between said answering station and said calling portable transceiver.