As I understand it, bear bells are simply one element in what is ideally a multi-faceted strategy of bear avoidance.  Basically you want mr.  bear to hear you coming - that goes double for mrs. bear.  Keeping a clean camp and hanging food and other odiferous items is also a major aspect of bear avoidance.

I remember vividly, when hiking in denli NP, my partner and I becme separated precisely at the point where recent griz activity had been recently reported.  Although I believe my hiking staff had a bear bell, I made sure I made plenty of noise as I struggled through dense underbrush to hook up with my buddy. No bears appeared.

Unfortunately this is the dreaded anecdote, but remember that the plural of anecdote is frequently data, beloved and cherished by all....

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