I used the incredibell when passing other trail users. It works for the 50% thad don't wear Ipods.
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For cagers or long-distance trail use (e.g., groups covering boths lanes of trail at 150 feet +) I'll break loose with the Airzound. Last week I encountered a group of about 10 that coated the trail 3 deep and let them have a dose of horn. The left half jumped to the right and the right half jumped to the left; both groups turned to watch me pass.