The theory is that severe thunderstorms which contain a tornado will also contain large amounts of lightning. The user was to turn the television to channel 13, turn down the brightness till the screen was almost black then switch to channel 2. As the tornado developed, the lightning intensity would increase to a point that would cause the screen to turn bright white since channel 2 is near the same frequency as the signal produced by the lightning and would override the brightness control. Conversely, not all thunderstorms which contain a large amount of lightning will always produce a tornado. Some television set are designed with filters to prevent this from happening.
Many people now have cable.
If you do, this will not work. This method produces far too many false alarms in the detection of tornados and also misses many of the tornados that do form. In homes and small buildings, go to an interior part of the lowest level such as closets, bathrooms or interior halls. Get under something sturdy. Don't even think about trying to escape from a tornado in your vehicle.