For years CATV has provided a one-way communications system. Many people have proposed an increase in the services offered to the subscriber by providing two-way communications utilizing the CATV distribution system. The uses and applications of such systems are limited only by one's imagination. The technical problems of two-way data communications system have been solved; hardware has been developed and is now available. Scientific-Atlanta's Security-Alert system is such a system.
The Security-Alert two-way data communications system was developed primarily for use in monitoring and reporting the condition of many remotely located transponder units (subscriber stations) to a centrally located interrogation unit (central station). The information to be communicated is digitally encoded and modulated on an FSK (Frequency Shift Keyed) carrier and transmitted over the CATV cable distribution system.