I spent the day teaching an update course for 911 dispatchers in California. Part of the course discusses PLB's, Tracme, and SPoT (and the advantages and disadvantages). And I recommend this site (among others) to them for further info.

For those who do not know, most 911 dispatchers in California are working 60-80 hour work weeks, because public safety agencies are not able to find or attract qualified employees for that job. If you would like to see the job up close, most agencies will let you "sit-in" the 911 center for a couple of hours to observe.
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"We are not allowed to stop thinking"