I've heard two sirens, producing 2 different tones, and I understand the reason for that (Santa Monica PD), but more than 2 IMO just confuses people, and possibly would cause rather than solve a problem. Multiple sirens are not necessarily louder, they just make more noise. I think that the sound pressure emitted from the combined devices will only be as loud as the loudest device, but a second tone, like wail+yelp or hi-lo, while approaching an intersection or congested traffic might help, and that's why true air horns are so useful. Am I correct on this, or am I way off? The often reported problem with all electronics vs a true mechanical is drivers can't readily tell direction of the EV approach. Multiple electronics won't help. This is why a mechanical tone siren, while it may sound better to many of us, probably cannot be heard any better than its effeminate , high pitched sister.