Monitoring apparatus using telephone link

Claim 1

Apparatus to establish two-way communications between a dwelling and a remote monitoring station using a telephone link and an existing automatic telephone dialer in the dwelling, comprising a microphone adapted to pick up sounds in the dwelling, a speaker placed in the dwelling, transfer means for effecting alternate, isolated connection of said microphone and said speaker to said telephone link, diplexer means electrically coupled to the dialer and responsive to a tone of a given frequency transmitted through said telephone link to activate said transfer means selectively to connect said microphone and speaker to said telephone link, microphone amplifier means between said microphone and said telephone link and adapted to amplify the output of said microphone, speaker driver means adapted to amplify signals from the telephone link and drive said speaker, and filter means for removing by filtering said tone of given frequency from said microphone amplifier means and said speaker driver means, said transfer means comprising an electromechanical relay having two contact positions, one of said positions connecting said microphone to said microphone amplifier means, the second contact position connecting said speaker to said speaker driver means, and means for selectively activating one of said microphone amplifier means and said speaker driver means, said electromechanical relay means and said selective activation means being operable simultaneously such that upon an emergency and the automatic operation of the dialer, a telephone link is established between the remote station and dwelling whereby said transfer means electrically couples one of said microphone and speaker to said diplexer means and electrically isolates the other of said microphone and speaker so that signals from the microphone are amplified by said microphone amplifier means and coupled into the link for transmission therethrough and signals from said remote station are amplified by said speaker driver means and broadcast by said speaker, thus establishing alternating voice communications between the dwelling and the remote station without interference by said tone previously removed by said filter means.