I find the round, thumb operated "bringgg, bringgg" bell works wonders. People instantly recognize it as a bicycle bell and just move over, usually without even looking. It has a pleasant tone, which is not obnoxious like an airzound.
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Il faut de l'audace, encore de l'audace, toujours de l'audace
1980 3Rensho-- 1975 Raleigh Sprite 3spd
1990s Raleigh M20 MTB--2007 Windsor Hour (track)
1988 Ducati 750 F1