I have also worked for several cable companies, specifically in their head-ends. Each cable TV operator is required to have EAS gear in their head-end that is capable of receiving feeds from federal authorities (via SAT) and local authorities via local AV insertion at head-end or hub. In Southeast Wisconsin for example, we built fiber into every municipality we have a franchise agreement with. This fiber is used to allow these municipalities to broadcast their village/town/city board meetings as well as broadcast local EAS info.

The commercial EAS gear in the head-end is made by several different manufacturers (Scientific Atlanta, Blonder Tongue, etc) and each manufacturer has a different way of scheduling and displaying mandatory weekly tests. This is why these messages always seem different from area to area across the country. Some equipment is older and some more modern. Some includes audio as part of their tests, while others do not.

All equipment has the ability to automatically and instantly override all channels of a cable lineup, whether using the IF loop of modulators (analog) or the mPEG streams of QAM encoders (digital) with the single broadcast feed from the EAS satellite receiver located in the head-end (messages from FEMA and other federal emergency government authorities.

Satellite TV providers (Dish, Direct TV) are even capable of offering this at a local level by taking advantage of "spot-beam" technology.

It's all pretty cool stuff.