Kenneth McClelland wrote:

If you're going to paddle at night (or anytime when there is a lot of boat
traffic) carry a loud whistle.


If it is large, fast traffic, I suggest one of those canned air horns under
the front straps. Use this first and keep the whistle connected to your vest
as a back-up. We may not be "Big" in the grand scheme of things but we can
at least sound big.

Another alternative is one of the "Safety Blaster" horns, which are lung
powered. They're MUCH louder than any whistle, but take less breath to
operate. Since getting one of these, I don't bother with whistles
anymore. There are two models. The larger one (commonly found at marine
stores) is too big for kayaking, but the smaller one will fit in a PFD
pocket.