Kind of beyond what you were asking about but my half dollar
suggestions.

Consider the "Safety Blaster Horn". Lung powered, 120dbs, 1 mile
range, $10. Do not try it out in enclosed space. I did. Could not
hear for 10 mins. Wife and I both carry one on PFD. All plastic, no
rust. URL below takes you Fogdog which sells them. Immersion in salt
water does not effect it at all - drain for 2 seconds and blow. Used
by us any number of times both on land and sea. Great for hiking if
separated by terrain.
http://www.fogdog.com/product/index....oductId=841305

Also the common garden variety cell phone in waterproof container.
Highly recommend AquaPac containers. Bought the ones we have in
London years ago but I believe that REI here in states sells them now.
Can personally attest to waterproofness in very gnarly Hawaiian
waters. We only paddle out if we have them on board. Have one for
each of the following; digital camera, cell phone, GPS, VHF and paper
nautical charts. May sound like overkill to many but our paddling in
Hawaii and other places tends to the extreme side and length. URL for
AquaPack below.
http://www.aquapac.net/

Last but not least is signaling mirror. Anything that helps the SAR
folks pinpoint your location, especially something that requires no
batteries, is worth having if it could save your life. Cheap, light,
and simple to use. There are endless tirades about which is better,
metal or plastic, which will last the longest etal. Just get one and
stick in the PFD. If you get caught up in "what type will last the
longest," buy a new one every year, they are that cheap. Is your life
worth $15 or so?
--
Big Island Bob