I was in Japan a few months ago and my phone woke me up making a sound I had never heard it make before and then the earthquake hit.
Pretty cool I got the notification a few seconds before I felt the shaking.
That's ETWS - Earthquake and Tsunami Warning System, a precursor to CMAS which I'm fairly sure started in Japan.
Yes, it can warn you before the quake is felt.
Yesterday during Tropical Storm Andrea, my co-workers with Sprint iPhones were getting these CMAS alerts throughout the day, but none of us with Verizon or T-Mobile got them (even though we have the option in Notifications to turn the alerts on/off).
Guess there are some other variables involved.
That sounds like a mis-configuration on Sprint's side (or on Verizon/TMobs side, but less likely).
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It all depends whether or not you are in that specific area. I believe it issues alerts based on towers, as opposed to your phone's GPS which is a good thing, saves battery life.
I have T-Mobile, and I got that alert yesterday, too.
VERY quick CMAS description:
* Warning agency (NWS for example) defines a warning area by drawing a shape on a map (circle, box, rectangle, etc), and warning text
* Cells that serve that shape transmit the warning message
That's it. The phone are always listening for the message, if you move out of the warned shape area, you won't get the alert.
Now, I had assumed that the co-workers in the previous reply were all in the same location. If not, that would explain the difference in warnings. Alternatively, if Sprint's cells were to be bigger, then the warning area will be bigger as well.
