Totally invisible unless you point them straight at the person looking for you, which is difficult to do with a laser when bouncing up and down in the water with a toy which isn't waterproof. Unless there is fog or cloud in which case the beam of light shows up, but the rescue crew can't see it due to cloud or fog.
Much better to stick to obvious ways of attracting attention
It's a gadget, so HWMBO has one. To be fair, we can light up even the very high clouds very easily. Hate to think what it would do to the eyes of a passing aircraft pilot. Believe me, it is surprisingly powerful. Got chased by a cross-channel ferry year before last; would have been very useful then. However, a torch worked, they were that close!