Safest bet is PLB, personal locator beacon that connects directly to satellites.
This link has a pretty good overview of the technology:
http://www.oceanmedix.com/oceanmedix...12-04-plb.html
There are many being made now, they seem to be about $300.00
http://www.thegpsstore.com/ACR-2880-...FYOk4AodHVYAtQ
Good luck