These little lites are very effective ~ they clip on easily to your Buoyancy Aid and are definately waterproof, I keep mine on my BA all the time and have carried out loads of capsize and rescue practices with them on. They are expensive and a small design problem is that to switch them on and off you need to turn the plastic cover which also releases the battery if you turn it too far. Having said that, you can be seen in the dark and other alternatives to kayak lighting are even more expensive, so just be careful I bought 2 and lost the cover on one about a year after having it, have just bought another one because I do quite like them ~ bit of a mixed review but can't think of a reasonably priced alternative.