Both horns and voice evac can fail to make people evacuate. Specially when people don’t actually see a fire (or other emergency), there is no punishment for not evacuating (like in school) and even the facility’s staff doesn’t care. See below for examples of all of the above.
Horns: https://www.youtube.com/watch?v=BpFUAQPt8Fs
Voice evac: https://www.youtube.com/watch?v=eIvuz8XEXVI
In the case of Walmart, and disregarding code, I wonder if the alarm might’ve been more effective if the SpectrAlert Advances were set to continuous at maximum volume, and the strobes’ brightness was cranked up a bit (say at least to 75cd, if they are spaced for 15cd).
The case of the concert also highlights another problem, which is that with such loud noise and so many flashing lights and fireworks, both horns/speakers and strobes can go unnoticed. Maybe for places holding concerts it should be mandated that strobes be 185cd (wall)/177cd (ceiling), and be spaced tighter than usual for such brightness. As for volume, that problem is harder to solve, since technically code already requires the alarm to be 5-15db louder than ambient noise, which for a concert is around 120db, but currently manufactured fire alarm horns don’t go above 90-100db, and I don’t know if speakers can go much louder than that. Perhaps another solution would be to require all of the concert’s speakers and visual effects hardware to be powered by a circuit that is automatically disabled upon fire alarm.