Having done my share of boating (27 foot sailboats and small motorboats in coastal waters, ocean kayaking, canoeing in Canadian wilderness, reading dozens of first-hand accounts of boating disasters, and many hours of monitoring VHF marine Coast Guard transmissions from coastal waters), I'm convinced that among the very best signalling devices are the large and expensive 25mm flares (day or night), and big orange smoke signals if the wind isn't howling during the day. Many times I have heard Coast Guard transmissions notifying that a flare was sighted in this and such area and investigations being initiated. Other signals can be easily overlooked and ignored, but those big 25 mm flares generally always mean someone's in deep doodoo (or soon will be if they've launched such a flare without being in any real danger). I don't count on anything less when on the ocean. Hand flares are excellent for guiding in rescue vessels from short range as long as they are held well away from the body and craft and over the water. But those 25mm flares are very bright and can be seen for miles, and really do attract attention.