I am interested in what kind of protection or defence is there against the drones. First is how would one detect them and how would one knock them out.
Can one make another drone that patrolls an area looking for these spy drones and then somehow shoots them down. Homes in on them then autodestructs...
A radar + a laser? An EMP device that would fry their electronics?
Would a small heat seeking missile work?
Well then there is always the moral side of it. If it is a plane with a human pilot in it, or a patrol car with a human in it, destroying it is equivalent to murder. Disabling or blinding one of these drones is just property damage.
You'd need to pick a scalable solution; where we have one drone today, we could have 20 in the same place for half the cost in the future.
In my opinion, the best solutions I can think of are:
1) EMP. May not shut off the motors, but should shut off the brains.
2) Base station with targeting system. Laser would be too slow, too dangerous. Maybe a high-powered water jet. Knock them right out of the sky. Break their wings.
3) A swarm of predator drones. Good ones would not be self-sacrificial.
I think a laser would scale much better than a water jet. Not to mention, isn't it hard to justify spraying water at every bird that flies by when you're stationed in a desert?
I think in the end, the cheapest thing will be something like a small gun mounted on turnable mount, with a camera attached. If it sees small something flying overhead, it shoots - normal airplanes will be too far up to hit, and if you have a lot of low-flying traffic, you could replace the bullets with rubber. Make certain - by physical means, not software - that the gun can't swivel below a certain angle to avoid shooting basketball players in the head.
You could probably use pretty standard ECM techniques to figure out what is a drone and what isn't by listening for their control signals. Of course that wouldn't help with autonomous drones, but those are still a ways off.
A laser sounds pretty good, they're big but you can swivel the beam very fast since you just have to move the mirrors. And they don't fall back to earth like bullets do.
EMPs are hard to produce without explosions of some kind[1], the energy requirements are similar to lasers but the power is way higher. They're hard to make directional, too, leading to a lot of collateral damage whenever you set one off.
"Of course that wouldn't help with autonomous drones, but those are still a ways off."
I can assure you that those are not a long way off. Fully autonomous drones can be deployed today by anyone with a few hundred dollars and a little electronic skills.
I think you'd just float some blimps with various sensors to watch for anything suspicious. [1] If you did spot anything suspicious, you'd simply move your high-value target as if you'd spotted someone with a gun or a suspicious bag in the area.
A jammer could be put into a ground-based vehicle and activated as part of a response, but even if you could engage a suspicious drone with your own, you'd still need to move the would-be target for safety's sake. So why bother?
[1] I'm rather surprised these things aren't already in use. They could be trivially disguised as promotional material for an event and even be tethered to provide superior power/data resources to your spotter blimp.
If jamming becomes common, it would take very little time for drones to be modified to be autonomous, or to follow a predetermined flight path if they lose contact with the controller. It might be effective now, and it gets points for being fairly easy to implement, but it's not going to be effective for long.
Can one make another drone that patrolls an area looking for these spy drones and then somehow shoots them down. Homes in on them then autodestructs...
A radar + a laser? An EMP device that would fry their electronics?
Would a small heat seeking missile work?
Well then there is always the moral side of it. If it is a plane with a human pilot in it, or a patrol car with a human in it, destroying it is equivalent to murder. Disabling or blinding one of these drones is just property damage.
Yes, this will be used as trigger to start a war: ( http://en.wikipedia.org/wiki/2008_Georgia%E2%80%93Russia_cri... ) but it is still far from killing a person.