Pretty sure bangers & spray are restricted items.  Definitely check with customs first.

I'm not too surprised that a car-alarm type noise has less effect than a banger.  Bangers make a percussive sound that's a lot more startling.

From what I've read spray is the most effective option when there's actually a black bear to contend with.

Old Joke:  How do you tell the difference between black bear & grizzly bear poop?
Grizzly bear poop has bells in it and smells of pepper spray.