I agree with Green, the Advance and TrueAlert have multiple frequencies, with the latter being higher pitched. I prefer the TrueAlert sound more, I feel like the Advance/L-Series, and in some cases the Integrity, sound more like alarms you’d hear in a really large factory buildings and stores, like Home Depot, Costco, or any Amazon building (those probably have speakers but whatever). The sound and aesthetic of the horn makes should relate to what area it would be placed in.