Emergency override system. The Local Access Alert (also known as Local Access System or Emergency Override System) is a system designed to warn radio stations, television stations, cable television broadcast feeds or satellite signals of impending dangers such as severe weather and other civil emergencies. With a gradual transition from analog cable to digital cable, the Local Access Alert has been phased out and largely replaced with the Emergency Alert System in the United States.

History
The first known Emergency Override Systems or Local Access Alerts were delivered during the boom of cable television in the 1960s, although it was not directly (and mainly) called the two main names of systems, as they sometimes pronounced it in various names. In the late 1960s and early 1970s, Local Access Alerts began to spread all over the United States, although few cities and towns had cable television yet. When cable systems continued to grow, the Local Access Alert was usually added.

Local Access Alerts gained the most popularity on local cable systems from the latter half of the 1970s until the end of the 1990s, when the Emergency Alert System took over the role of the Emergency Broadcast System on cable television on January 1, 1997. The Emergency Alert System began to build up on most cable television systems through the installation of then-new generators and encoders between 1997 and 1999. Some of the notable EAS generators at the time include Video Data Systems, Texscan, Gorman-Redlich, Idea/Onics, and Cable Envoy; and encoders include SAGE, TFT, and Trilithic models. During the cable growth of the Emergency Alert System, only some cable systems retained the Local Access Alert equipment up into the first part of the 2010s.

In the late 2000s and early 2010s, most remaining cable systems set up for Local Access Alerts used either both Trilithic EASyPLUS or Video Data Systems as their modern screens instead of the previously used older systems such as CommAlert (although older systems of the Local Access Alert were still used in a handful of areas at the time). By the end of the 2010s, the popularity of Local Access Alerts became nearly extinct on most cable systems in the United States, as all cable systems already had the Emergency Alert System, which at that time, local cable systems had become either Comcast, Time Warner Cable, or Suddenlink among others.

As of the early 2020s, most Local Access Alerts are delivered as practice or demonstration warnings as part of the Emergency Alert System, but the remainder of the nearly-extinct Local Access Alerts can still be seen on a minority of very small cable systems that either haven't had equipment upgraded or became part of a major company in unincorporated or very minor areas.

Purpose
Police or emergency management let cable viewers in local and surrounding areas know of an impending emergency and instruct them to shelter or evacuate. Alerts are chiefly for weather warnings for severe weather such as tornadoes, flash floods, earthquakes, winter storms, and hurricanes. Alerts may also pertain to Amber alerts, traffic closures, 911 outages, forest fires, dam failures, train derailments, and road conditions.

Activation procedure
The Local Access Alert is initiated by local law enforcement or emergency management staff, much like the antiquated Emergency Broadcast System, by dialing a number and entering a PIN through a telephone to take control of the cable of an area in the path of danger. Cable subscribers in that area have every television channel interrupted by audio and often a given screen. The distinct attention signal played can be Morse code, a siren, DTMF tones, steady single (or dual) tones, or multiple hi-lo beeps. The screen shown can be black, white, colored depending on warning, a slide or static. More modern alerts use a black screen with the words "Local Access Alert" in all capital letters with a message stating that "a local authority has initiated a direct community access"; the text was generated using the Trilithic EASyPLUS character generator (the same one used for the Emergency Alert System).

System tests
Tests of the Local Access Alert occur once weekly at randomly selected times, as well as scheduled monthly tests and yearly tornado drills. These alerts resemble the format used for activation of the Emergency Broadcast System and the Emergency Alert System.

Limitations
A limitation of the Local Access Alert system is that operators have to dial out to end transmission. Simply hanging up the phone connected to the system after an emergency broadcast does not work, and viewers may hear other phone noises – such as off-hook tones or dial tones – before cable programming resumes.

The newer Emergency Alert System employs Specific Area Message Encoding technology to activate for potential disasters and deactivate to resume cable broadcasts, especially late at night when many public servants aren't available to break in.

References

United States civil defense
Disaster preparedness in the United States
Cable television
Warning systems