I have an Air Zound. I mounted it on my Bike Friday for riding after my dog accident where I fractured my pelvis in three places. It is loud and not very attractive (definitely increases the fred quotient exponentially! ), but it works well. I have used it a few times to deter dogs, and only one seemed to ignore it. He may have been deaf.
There is a volume control. If you are riding with others, warn them that you have it and if you can, before you use it, as it can be startling. I am sure someone in a car could hear it too, but I haven't had to use it for that yet.
Emily
Emily
2011 Jamis Dakar XC "Toto" - Selle Italia Ldy Gel Flow
2007 Trek Pilot 5.0 WSD "Gloria" - Selle Italia Diva Gel Flow
2004 Bike Friday Petite Pocket Crusoe - Selle Italia Diva Gel Flow