You might also consider one of those Airzounds air horns. I actually used it a couple of weeks ago to get the attention of a police officer at night, and I'm glad I had it. I don't shout too loudly.
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"Real wars of words are harder to win. They require thought, insight, precision, articulation, knowledge, and experience. They require the humility to admit when you are wrong. They recognize that the dialectic is not about making us look at you, but about us all looking together for the truth."