I have found cats hung by their own collars, dead on fences.

Do not put collars on your cats.  They frequently become entangled -- some
have strangled on the collars.  I would not even trust the breakaway
collars.  Moreover, cats learn to walk carefully so that the bells soon are
not effective.

I don't want to stir up a hornet's nest here, but my recommendation is to
keep your cats indoors (especially if you live in the US).  Your cats will
be much safer, and they will be equally as happy if you provide cat trees,
scratching posts, and plenty of toys.

MaryL

They don't work at all, it's an urban myth. Cat collars are basically an
un-necesary health risk to the cat which are ultimately promoted because
they make your cat look 'cute'. My 3 are in/outdoor cats and do what is
natural to them & hunt little things which they bring back home (Teal'c has
recently found a nest of frogs which he is slowly depleting). Anyone who
doesn't like this should buy a vegetarian pet rather than hinder their
'loved' one's natural instincts. :)

The kittens will stay away from your neighbors' dogs. The smells
from the dogs marking each territory will trigger this.

I've used breakaway belled collars for the last fourteen years on
both my tabbies. Neither has hung himself nor has the bell alerted
any animals. (No collars or cats have been found hanging from any
fences in my neighborhood, either.) The bells do give each of my
tabbies something to gnaw upon, though... They love attacking the
bells on each other's collar -- even at fourteen yo.

The bells will alert you to when they climb counters for that
early-ay-yem pat of butter or explore the top shelf of your china
cabinet, though...

The Ranger