its called Megazorn. I think there are other types but this one takes a 9v square battery and you mount it anywhere you want. About the size of a cigarette pack. Pretty small and convenient Has a small button trigger. Will work on any bar. I have the horn mounted to my bagstrap and the trigger I rigged to the tip of my finger. works really well and I can hop off the bike and it comes with me. Although i'm trying out diferent ways to mount it. maybe just use electrical tape to tape the whole thing to the top tube. It's loud as **** like the police horns. i've had a few good laughs already watching people **** their pants when I use it.