I have used both the Fox40 and the Storm.  I think the Storm whistle is louder, but it is about 4 times bigger than the Fox.  I carry a modifed Fox (see Doug's instructions) around my neck and in my PSK.  I keep a Storm in my Daily carry kit, coat pocket and CERT response kit.  I find the Storm great for canoeing, backpacking etc, but too bulky for EDC.<br><br>

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 Storm Whistle