This begs a question; why did White Noise emergency vehicle sirens not take off?  They're as rare as rocking horse poo!!,(reply>), White noise alarms will not penetrate or bounce off surfaces like glass, walls etc. in the same way a beeping alarm does, and as such they are not suited for emergency use like on an ambulance. Which is kinda the point, they don't pollute the surroundings with unnecessary noise that travels all over the place. Broadband noise works very well for backing alarms, and I wish more trucks start using them. Just the beeping from garbage trucks alone wakes up half the city every bloody morning.,(reply>), @TalesOfWar The fact white noise is directional is the reason why I'm surprised White Noise sirens didn't take off.  I appreciate a reversing vehicle alert is more commonplace than an emergency vehicle, but the problem of a non-directional sound is still there. I often hear emergency vehicles long before they come into view and wonder "where the hell is it coming from".  If white noise sirens were used, it would arguable answer that question a lot sooner.