If they designed the system (hopefully at the hardware level) so that it was incapable of recording voices I would have no problem with it.
That would probably be a good thing for a competitor to create: a shot detection system that's designed to address civil liberty concerns. I bet someone on HN could do it.
If you do that simply by damping wavelengths of speech, you possibly make opportunity to alter the sound of a gun so that it doesn't set the alarm of. Maybe more importantly the sound of a gunfire would not sound like anything familiar to human ear, so it would make it very difficult to manually pick the real shots.
But the problem is how can you verify that the system that is actually installed on all the building and telephone poles is actually one that is incapable of recording voices instead of a (really cheap) normal microphone.
That would probably be a good thing for a competitor to create: a shot detection system that's designed to address civil liberty concerns. I bet someone on HN could do it.