Been here done this........the bell that come on a cat collar doesn't seem to make enough noise for some animals cats hunt.

This is what I do.....I get those small cow shaped bell that come on bird toys, they have a stronger ring to them. This has worked great for me for many years. I've watched them hunt and soon as they try to pounce the bell sounds and off goes their prey. After a while I even noticed that some of my cats don't even try any more, maybe they think they lost their touch.