Called "a quacker" or reversing quacker in Australia, very effective, and ubiquitous. Unfortunately the sound didn't come through clearly, it's actually very obvious when you hear it, and at the least it makes you look in the direction of the vehicle even if you don't associate the sound with a reversing truck. <br><br>Many commenters claiming they've never heard them before - which means two things; the less obtrusive function is working, and you haven't been on a safety construction site recently.