Re-read it, Brian. It does not appear to be a P-wave detector. The article states: "Using the early warning system network and data provided by Japan's Meteorological Agency (JAMA) via the Internet, the appliance sounds off a loud countdown of up to 20 seconds to the moment the tremor begins."

Though the sentence doesn't parse (what does "up to 20 seconds to the moment the tremor begins" mean?), it can be deduced that the Internet warnings are sent out to the device once a computer algorithm determines that an earthquake has actually occurred. In some ways superior to a P-wave detector, but probably providing a little less of the already minimal warning time (due to additional processing seconds necessary to confirm a quake has occurred).

But, this brings up other questions. Why 20 seconds? Theoretically, it could give an hour's warning. But only to people who are so far away that the quake could only be detected instrumentally. I think the 20-second figure was chosen as representing the time available to people at the maximum distance where significant shaking might occur. If the signal was sent out instantaneously, with no processing time, then 20 seconds corresponds to some 75 miles or so of S-wave travel time from the epicenter. With processing time, if a maximum of 20 seconds is provided, then that figure might be maybe 100 miles or so.

I think the P-wave detector might be a better deal, as it's faster, if you are willing to accept more false alarms. But the new device would be interesting for people who just want to know rapidly anytime a quake has happened somewhere in or near the Japanese Islands.
MW
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