I could have sworn an EAS topic already existed, however I cannot find it, so I will reply here....
In my area, on Comcast, the way the EAS comes through differs if you're on a cablebox or direct cable or CableCARD...
If you're on a CableCARD, such as myself, then you will see a scroll. The TiVo throws you back to live tv, if you're watching a recording, and it will throw up a scroll that you are NOT able to exit out of, and no button presses will work. The issue with this is that once the scroll disappears, the CableCARD has to retune to the channel, thus affects some of my recordings if both tuners are in use.... There is no audible tone that comes from Comcast if you are using a CableCARD in my area (with the exception of if a local station chooses to do so, that will come through directly from themselves).
If you are on a cable box in my area, you will hear the EAS tones, and a scroll will also appear at the top of whatever channel you are on. Again, you cannot exit out of the scroll, but you can still use your guide and what not, including changing the channel, and you will still see the scroll going through. Same local station exceptions apply.
If you are on a direct cable feed, you will hear the EAS tones, and you will hear a message saying to tune to channel 2 for emergency information, whether it be a test or an actual warning. Same local station exceptions apply. Channel 2 is our local organization channel for county wide stuff, like events and such. We do have channel 19, but Comcast does not control that channel, thus nothing usually goes through there except local community and school stuff.