Comment Cox Communications (Score 5, Informative) 451
I was watching the test on a friend's Cox Communications cable service, and they also switch to a shopping channel (cable channel 8) for emergency alert activations. Their cable system apparently is incapable of showing the alert on all the (digital?) channels, so they simply show it over analog shopping channel 8 and have a system in place to switch everyone to that channel automatically whenever an alert is triggered. It's a bit annoying if a test is scheduled during, say, an important football game... er... episode of Mythbusters... whatever. On the other hand, it is even more jarring than the alert tones, so you'll certainly know something's afoot.
If you have one of their Motorola digital cable boxes, when it goes into emergency alert mode and auto-switches to analog shopping channel 8 for the message, the front clock display changes to "EAS" as well. If you're suddenly watching the shopping channel and "EAS" is displayed on the cable box *and* you have the wonderfully annoying (and intentionally so) alert tones, you *should* be able to figure out that now's the time to read or listen. At least, that seems to be the general idea.
I did notice that I didn't get the alert over cable until after I'd finished watching it on OTA TV (and chatting about it afterward), so chalk up a minute or two of additional latency to the cable company.