scription programs may be selectively individually displayed on a common display channel provides premises access monitoring in addition to such display. A multiplexed communication signal containing a plurality of different program information signals and a plurality of command signals is provided to a plurality of display devices which are capable of substantially simultaneously displaying different selected program information displays from the plurality of such signals in response to selected program information signals. Each display device has an associated means for controlling the selection of these programs which is connected to a common condition responsive means, such as a computer. The control means includes means for demultiplexing the communication signal and for generating a given program information selection control signal in response to a uniquely identified command signal which control signal, when mixed with the demultiplexed plurality of subscription program information signals, provides the selected one at the frequency of the common display channel. The computer and common communication signal path thereto are utilized to provide premises access monitoring, in which instance an optical card reader utilizing fiber optics provides input conditions to the computer indicative of both the status of the door to the premises and the authorization of the entrant, a randomly selected insertable card providing the information to the computer through the reader. Such reader may employ a modulated light source, light polarization, or space and/or time diversity in order to increase the security of the reader. In addition, a pair of separate input devices, such as a card reader and a door position sensor may be utilized for such monitoring.
32 Claims, 13 Drawing Figures