RE: Realistic Aims

Despite the fact that it would just be really cool to have some sort of device that could disable an attacker, I just can't get around the pure logistics of how it could be implemented on a wide scale. Just think of how many colleges and high schools there are in the U.S. Not only would the rooms have to be protected, but the hallways and other common areas also. Then there's every other place that people gather that would be the next target. (Stadiums?) The shear numbers and expense as you mentioned would probably keep it as nothing but a pipe dream even if the technology did exist.

Electricity, especially in the high voltage range needed to bridge an air gap is very unpredictable as far as aiming goes (think of lightning zigzagging across the sky), and could have widely varying effects on each person if it even hits them in the first place. According to this table, current as low as 20mA can stop a persons heart. The physical effects listed from lightning, which of course is what "electrodes shooting out of the walls" would have to really be, would be enough to never let the project get past the lawyers. Another way electricity is used these days to disable people, is with a TASER which either shoots a dart connected to the gun with thin wires, or operates at close range as a "cattle prod". I don't see how automatic projectiles would be reliable enough to either disable everyone, or just an attacker on a 100% basis; which is what it would have to be to be worth implementing at all. All of these then would have to be activated somehow. Being triggered by a gunshot is an interesting idea until someone's motorcycle backfires or something.

All in all, the knockout gas idea (theoretically) has more merit for implementation, except there are also probably more ways to bypass the effects.

All of the above is just rumination on ideas that won't go anywhere soon. I guess in a way, it's a bit of a comic book sort of dream to want to be able to thwart something so deadly and evil either with super-human means or "ultra-technical" means. How many of us have imagined ourselves in one of the afflicted Virginia Tech classrooms; half fearing and half fantasizing what we might have done in the same situation? (I imagine myself picking up a desk or chair and rushing at him blocking bullets all the while... Yeah. Right. Maybe.)

In the end we have to devote our energy into social systems that catch these guys early if we ever want to stop it from happening again. Getting someone on "the list" who needs to be would be a good first step.