I used to use a bicycle horn to get my kids attention. I had a
friend who used a duck call. Another taught her kids a secret word,
and whenever she said the word "states" they froze. I used the
secret word "biomorphic" at one school and "dodecagon" at another
school after I watched her kids in action.
Whatever you use, you will have to teach the students how to react to
it. Make a sign for your cart that says "Ms. Watkins Horn = Silence."
Inform them of consequences of not being silent when your horn honks.
Practice. Have them pretend to talk "walla-walla-walla-walla" and
tnen honk the horn and see if they get silent. Try it several times
the first class. Remind them the next class. Be willing to help
students accept the consequences if they can't be quiet.
At the end of the year last year I let my students honk my horn (they
were not allowed to touch it during the year) on the last day of
school. I think they liked it.
Hope this helps. You're bound to get some good stuff of this list.
Assistant Professor, Art Education
University of Central Arkansas
Department of Art
Conway, AR 72035