Personally, I've had good experiences installing the "S" box detectors. I think they are pretty good with a minimum of false alarms.
Oddly enough, I got a call from a guy last week asking about one I recently installed in Pomona, CA, because it had triggered. Couldn't find anything at USGS or SCEC to substantiate a trigger. Since it records events, I'll look for what caused it.
Cheers!

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