YSK: bear bells are largely ineffective at keeping bears away
Why YSK: effectively identifying yourself to bears is paramount when in brown bear country. Bear bells are not great at that.
You've seen them in outdoor stores and heard them on the trails: little jangly bells that attach to your gear and make noise so you don't surprise a bear. Easy peasy, right? Well, not so much...
They are not really all that loud. If it can't be heard from a few switchbacks away, it's not loud enough to alert bears at a distance. They're certainly not louder than running water if you're hiking near a river.
Bears don't know what that sound is, and therefore don't associate it with danger. Human voices, cracking branches, loud sudden noises? They know to head in the other direction. But soft jingles? There's nothing in that sound that would trigger a bear to leave the area. They know what danger sounds like; a little bell is not an alarming sound that would instigate the flight reaction you're looking for.
Repetitious sounds become easy to ignore. Animals (humans included) are much more likely to react to an irregular sound, like a sudden shout, than a soft, repetitive jingle. Bells run the danger of becoming background noise.
So what should you do? If you're in a group (recommended), make sure you're talking amongst yourselves. If silence is what you're looking for, AT LEAST give a good shout every five minutes, especially if you're cresting a hill, coming 'round a bend, entering brush, or in some other situation where visibility is limited. If alone, intensify these efforts and make it a game. I like to very loudly list all the Pokémon I know...it usually gives me a few hours of content (yeah, yeah, I'm a nerd). And remember to be loud and shout it out-you have to be much louder than a bell. You might feel a bit crazy, but it's the best way to be safe in bear country.
Remember: the vast majority of bear attacks are defensive as a result of surprising a bear. There's no need to hike in fear as long as you're taking the correct steps to respect these animals. And always carry your bear spray. Happy hiking!
Source: park ranger who does a lot of solo hiking in brown bear territory. Also tired of hearing people jingle-jangle through the visitor center 8 hours a day.
TLDR: bear bells are neither loud nor alarming enough to keep you safe from bears. You're better off using your own voice.