A quick google search, "GPS TRANSPODER" turned up a lot of reading, but one of the first was for a marine GPS Transponder, SPOT, with 911 help if you wanted. The price was $129 and it looked about the size of a cell phone. Interesting I'll bet it won't be long before GWS has a 2 oz unit for $39.95 for our models.

Don

Just found this first at tower then to the web site.
http://www.eagletreesystems.com/
Not quite $39.95 though but super neat

Don