Maybe some company is working on this, but I have an idea

[Ferrets are Cool]

Why not employ miniature drones with an aerosol or some sort of spray that would incapacitate active shooters. I'm sure the logistics of how to utilize drones in this manner would be fairly easy to overcome.
Find the negatives.

After typing this, I found this web page...unfortunately, it is being developed for military bases only.
https://thecrimereport.org/2022/06/07/drone-technology-to-deter-active-shooters-gets-air-force-ok/

The U.S. Air Force has awarded defense technology developer ZeroEyes a $750,000 research grant to develop and deploy a “Drone-Robot Enabled Active Shooter Deterrence” at Ellsworth Air Force Base in South Dakota, using drones to respond to active shooter threats on the base, reports Yahoo Finance.

[sl8]

1. Axon had plans for a Taser drone, but they're on hold.

https://apnews.com/article/technology-government-and-politics-shootings-655fc0df3588e3e6afcd2a81b9619724

Axon halts plans for Taser drone as 9 on ethics board resign

[Ferrets are Cool]

2. Yeah, I saw that. I like my idea better.

[Midnight Writer]

3. There are drones not much bigger than a mosquito that could be used to surveil the miscreants.

Or they could simply buzz around the perpetrator's head making noise. Any time the shooter is swatting at drones is time he is not shooting people.

I also think the idea of robots entering the zone has potential. Even if the robot is not capable of stopping the shooter, it will freak him the fuck out, and any time he spends shooting at robots is time he is not shooting people.

[Samrob]

4. In the wrong hands, it could incapacitate law enforcement...although they do that on their own., nt

[Ferrets are Cool]

5. You mean like guns.

I wish I had the capital to get this off the ground.