She's indoor/outdoor gray cat.  Hard to see except in broad daylight.
First the bell lets me know she underfoot and keeps me from breaking
my neck.  I got tired of tripping over her all the time.  Even with
the bell I stepped on her today when she was lying around.  Lucky I
was able to stop before putting my full weight on her.

Also she doesn't always come when I call.  Before the bell there were
times when I stood at the open door calling her only to find out later
than she had snuck passed me into the house.

The collar breaks away.  Don't know where the first one was caught but
she came home one day without it.  Perhaps being a long hair make the
collar more comfortable.  I had a short hair cat who would not wear
one.