It doesn't prevent all mass shootings, no. It may improve police response times, or if there is an officer at the school it may alert him. Improving police reaction time may save lives.
It could also sound a warning for the school so that students could preemptively run or hide. Imagine this system hooked into the lighting and lights in the immediate vicinity of the shooter could turn a dangerous red, yellow nearby and green along routes that would escape the shooter. Students could evacuate more easily if they could trust that system. Another innovation might be strobe lights that could focus on the attacker to disorient and distract him.
I think there's a huge responsibility to such technology and much danger to it, but there are potential uses.
Yes, but the reaction time is "after" the alarm, the point I was trying to make is that this surveillance/weapon recognition approach may trigger the alarm earlier (of a couple minutes, maybe 5) but if the reaction time is in the tens of minutes range, it would make no particular difference in the actual outcome as all the shooting will happen anyway before the police can arrive.
About the trust on the system, it's tricky business, as always, the amount of false positives need to be reduced to 0 or next to 0 to gain trust, and it is very unlikely, besides the errors of the system, like innocent maintenance people - say - plumbers or electricians carrying pipes or tubes, or some power drills, etc. (let alone carpenters with nail guns) I would bet that the new rage among the school kids would be finding perfectly legal items (let's say for the sake of reasoning antennas, cactuses, umbrellas) that would triggger the alarm, just for the fun of it.
Good point about alternative "distracting" means (lighting colours, strobe lights etc.) but again, when (hypothetically) such a system will be installed I doubt that it can avoid daily, weekly or monthly false alarms and after a given number of them happens, usually the system is disabled or - if possible - set to very low (ineffective in practice) sensitiveness.
A big reason that the false positive rate needs to be around zero is actually how uncommon school shootings are. Just a few false positives erode trust in the system and make people turn it off.
The problem is black swan events[0] are really hard to predict
It could also sound a warning for the school so that students could preemptively run or hide. Imagine this system hooked into the lighting and lights in the immediate vicinity of the shooter could turn a dangerous red, yellow nearby and green along routes that would escape the shooter. Students could evacuate more easily if they could trust that system. Another innovation might be strobe lights that could focus on the attacker to disorient and distract him.
I think there's a huge responsibility to such technology and much danger to it, but there are potential uses.