My Norco has a Tektro brake lever with integrated bell:



It's not as loud as the Incredibell knock-offs that I have on my other bikes, but it looks way cooler. I use an Airzound to get the attention of those who can't hear (or ignore) my bell. It even works on the MUP - I once used the horn to warn a city worker who was clearing clippings from the path with a gas-powered leaf blower while wearing ear protection. Two short blasts and he jumped out of the way with a deer-in-the-headlights expression on his face. Airzounds rock!