115 decibels, just in case… The Airzound is a VERY loud bicycle horn using compressed air (which you can pump in via your bike pump, Schrader valve). I usually start with the “standard bell” (the black one, right above the grey Airzound), and only if it is not enough or people just do not 
care (which sometimes happens, yes !), then I go for the 115 db. Only with cars, I start right away of course with it. I like to honk a car in a traffic roundabout, thinking I arrive much slowier and cutting my priority !
The horn is fixed on my right handle bar (see picture above), the air bottle is arranged right under my seat (see picture below).