Abstract: A telecommunication and alarm system for connection to: a four-wire or two-wire telephone network, a two-terminal doorphone unit, and one or more alarm detectors connected in parallelCOMPRISINGa line and extension connection for communication with the "tip" and "ring" wires of the incoming telephone line and the service pair of wires enabling in-house plug-in installation of the inventive device; and an alternate extension connection for communication with the "tip" and "ring" pair of the telephone wires leading to the in-house single-line extension telephones;a plurality of connection modules each equipped with a slide entry plug and a slide entry jack, the plug end of which to be inserted within the telephone wall outlet, and the jack of which to receive the telephone cord of the extension telephone set;an input connection for unidirectional communication with a two-terminal doorphone unit, from any in-house extension telephone, and means to toggle the direction of speech upon pulsing one same digit on the