I've kept a small canned horn, which is quite loud, on my bicycle handlebars for several years. When I ride the bike I use a bike path so that I can avoid riding in the streets, and often come up behind walkers or runners who are totally oblivious to what is around them. Their earbuds or headphones are often loud enough for me to hear what they are listening to. So when I call out from behind them "On your left" or "Passing you" or whatever, there is no response at all. Several years ago I was knocked to the ground by one of these jerks deciding to move left without looking behind him just as I was passing. Both of us ended up on the ground with minor injuries. Since then I carry this horn and have had to use occasionally and trust me, it gets the attention even of the jerks with their music blasting in their ears. One woman accused me to trying to give her a heart attack, to whom I responded that if she walked all the way on the right of the lane I would not have used the airhorn, but since she chose to walk right down the middle I had no choice. She told me to drop dead, and I responded politely with the one finger salute as I continued on my way. That horn is also great at sports events.