Abstract: This invention relates generally to use of standard video scan lines of commercial television programming in a cable television system for transmitting alerting and other messaging information, to an alert receiver unit at an end user's address. The alert receiver unit operates completely independently of any television set at the end user's address, other than to send the CATV signal from the alert receiver unit to the television set. The subscriber or other user can send certain pre-selected signals to the operator of the cable TV system, to another subscriber/user, or to another recipient designated by the operator of the cable TV system. The invention relates especially to emergency notification systems and to systems for communicating emergency messages to subscribers to cable television distribution networks, as well as to non-subscribers.